Method for continuously purifying ethyl maltol

Abstract

The invention discloses a method for continuously purifying ethyl maltol, and particularly relates to the technical field of production of flavors and fragrances. The method performs purification operation based on a purification device, and comprises the following steps: continuously adding an ethyl maltol crude product into a reduced pressure distillation device to obtain an ethyl maltol crystallization raw material; ethyl maltol crystallization raw materials enter a dissolving device to be dissolved in a mixed solution of ethyl alcohol and water, and an ethyl maltol to-be-crystallized solution is obtained after dissolution; the ethyl maltol to-be-crystallized solution enters a multi-stage crystallizer through a discharging branch pipe to be crystallized; and overflowing liquid of the discharging branch pipe of the last-stage crystallizer enters a post-treatment device, and is filtered, washed and dried by the post-treatment device to obtain an ethyl maltol product. According to the method for continuously purifying the ethyl maltol, the continuous purification of the ethyl maltol is realized, the operation is simple and convenient, and the obtained ethyl maltol product is high in quality and good in fragrance; the one-time crystallization yield of ethyl maltol is stabilized to be 90% or above, and the purity is 99.9% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of essence and flavor production, and particularly relates to a method for continuous purification of ethyl maltol. Background Art

[0002] Ethyl maltol is an important flavor enhancer, with functions such as enhancing fragrance, enhancing sweetness, preserving fragrance, "ripening", anti-corrosion and masking off-odors. Its fragrance-enhancing effect is six times that of maltol (i.e., methyl maltol), and it is widely used in industries such as food, beverage, toothpaste, cigarettes, cosmetics and pharmaceuticals. In 1970, ethyl maltol was officially listed as a food additive by the World Health Organization and the Food and Agriculture Organization of the United Nations. With its significant fragrance-enhancing effect, recognized safety and wide application, it has developed rapidly at home and abroad.

[0003] Currently, in China, ethyl maltol is mainly synthesized by the furfural method. This method uses furfural as the raw material, and is widely used due to the advantages of easy availability of raw materials, low cost, simple process and less three wastes. In this process, furfural first reacts with Grignard reagent to prepare ethyl furfuryl alcohol, and then ethyl furfuryl alcohol is synthesized into ethyl maltol through processes such as electrolysis, acidification, oxidation and hydrolysis. At present, China has been able to well master the synthetic technical route of ethyl maltol, but lacks in-depth research on its refining technology. The operating temperature in the refining stage is relatively high, the product yield is low, the product quality is unstable, and the market competitiveness is poor. Currently, the conventional refining process is to sequentially subject the crude ethyl maltol to sublimation and crystallization to obtain the refined solid ethyl maltol.

[0004] Chinese Patent CN109513232A discloses an evaporation crystallization device for the crystallization of ethyl maltol. After continuously injecting the raw material liquid into the raw material liquid inlet pipe, the preliminary separation of ethyl maltol can be achieved through steps such as evaporation, crystallization and shunting. This patent only uses the evaporation crystallization method to purify the crude ethyl maltol, and the obtained ethyl maltol product has a low purity and needs to be further refined to obtain a qualified ethyl maltol product. Moreover, a large amount of organic solvent needs to be evaporated during evaporation crystallization, resulting in high energy consumption.

[0005] Chinese Patent CN109851603A discloses an ethanol continuously recyclable ethyl maltol preparation system, including a sublimation device, a crystallization device and an ethanol mother liquor recovery device. After adding an appropriate amount of ethanol to the crude ethyl maltol and crystallizing it in a crystallization kettle, the solid ethyl maltol product is obtained by centrifugal separation. The obtained liquid is the ethanol mother liquor containing ethyl maltol. The ethanol mother liquor is distilled to recover ethanol, which can be reused for the crystallization of crude ethyl maltol, and the distillation residue is returned to the sublimation section to recover ethyl maltol. However, this process still uses the traditional sublimation process, with a relatively high operating temperature and low efficiency in removing low-boiling impurities, which affects the quality of the final product.

[0006] Since ethyl maltol is a thermosensitive compound, a relatively high sublimation operation temperature will result in significant heat loss. Moreover, the operation process is intermittent, with high labor intensity, unstable quality of the crystalline product, difficult control of unorganized emissions during production, low production efficiency, and high energy consumption. Summary of the Invention

[0007] To this end, the present invention provides a method for continuous purification of ethyl maltol to solve the problems in the prior art.

[0008] In the present invention, the crude ethyl maltol is subjected to continuous vacuum steam distillation to remove low-boiling impurities with pungent odors, and then continuous vacuum distillation is carried out to remove high-boiling impurities with darker colors, obtaining a crystalline raw material of ethyl maltol. Then, a crystallization solution of ethyl maltol is prepared by mixing ethanol and water in a certain ratio, and it is successively crystallized through 3 to 6 continuously connected kettle crystallizers. By controlling factors such as the feeding speed, crystallization temperature, and stirring speed, a stable suspension of ethyl maltol is obtained, and after filtration, washing, and drying, an ethyl maltol product is obtained. The process of the present invention removes low-boiling impurities with pungent odors through continuous vacuum steam distillation, removes a small amount of high-boiling impurities with darker colors through continuous vacuum distillation, and ensures product purity through continuous crystallization and washing. The entire refining section can operate continuously, with stable product quality; the obtained ethyl maltol product has high purity and good aroma; the processing efficiency is high, and it is suitable for large-scale continuous production.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] According to a method for continuous purification of ethyl maltol provided by the present invention, purification operations are carried out based on a purification device, and the device includes:

[0011] The system includes a vacuum distillation device, a dissolution device, a multi-stage crystallizer, and a post-treatment device connected in sequence; among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol; the outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and is in communication with the dissolution device; the dissolution device is also provided with a discharge branch pipe, which is connected to the next-stage crystallizer, and the discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device;

[0012] The method includes:

[0013] Step 1, continuously add the crude ethyl maltol into the vacuum distillation device, and successively carry out vacuum steam distillation and vacuum ethyl maltol distillation to obtain a crystalline raw material of ethyl maltol;

[0014] Step 2, the crystalline raw material of ethyl maltol enters the dissolution device and dissolves in a mixed solution of ethanol and water, and after dissolution, a crystallization solution of ethyl maltol is obtained;

[0015] Step 3: The ethyl maltol crystallization solution enters the multi-stage crystallizer through the discharge branch pipe. Start stirring. When the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the second crystallizer. Start stirring, and the multi-stage crystallizer repeats this operation;

[0016] Step 4: The overflow liquid from the discharge branch pipe of the last-stage crystallizer enters the post-treatment device, and the ethyl maltol product is obtained through filtration, washing, and drying in the post-treatment device.

[0017] Furthermore, the vacuum distillation devices are all tower equipment, including a steam distillation tower and an ethyl maltol distillation tower; the crude ethyl maltol is fed from the upper part of the steam distillation tower, and steam is fed from the lower part of the steam distillation tower. To ensure sufficient contact between the crude ethyl maltol and the steam, the packing between the two feed ports has 10 - 20 theoretical plates.

[0018] Furthermore, in Step 1, the addition ratio of deionized water is 3 - 5% of the mass of the crude ethyl maltol.

[0019] Furthermore, in Step 1, during vacuum steam distillation, maintain the kettle temperature at 100 - 110°C and the pressure at 4 - 6 kPa; the temperature of vacuum ethyl maltol distillation is 130 - 150°C and the pressure is 0.05 - 0.5 kPa.

[0020] Furthermore, in Step 2, the mass ratio of ethyl maltol: ethanol: water is 1: (1 - 1.5): (0.5 - 1.5); the saturated dissolution temperature is 30 - 36°C.

[0021] Furthermore, in Step 2, keep the temperature of the ethyl maltol crystallization solution 5 - 10°C above the saturated dissolution temperature.

[0022] Furthermore, in Step 3, the temperature in the first crystallizer is 1 - 3°C below the saturated dissolution temperature; let ethyl maltol form crystal seeds under slow cooling; the total number of crystallizers is 3 - 6, the temperature in each stage of the crystallizer is 1 - 8°C lower than that in the previous stage of the crystallizer, and the temperature in the last-stage crystallizer is 22 - 28°C lower than the saturated dissolution temperature.

[0023] As an example, preferably, the temperature in the second crystallizer is 3 - 5°C below the saturated dissolution temperature; when the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the third crystallizer. Start stirring and control the temperature in the third crystallizer to be 5 - 10°C below the saturated dissolution temperature;

[0024] When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the fourth crystallizer. Start stirring and control the temperature in the fourth crystallizer to be 10 - 15°C below the saturated dissolution temperature;

[0025] When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fifth crystallizer, the stirring is started, and the temperature in the fifth crystallizer is controlled to be 15-21 °C below the saturation dissolution temperature;

[0026] When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the sixth crystallizer, the stirring is started, and the temperature in the sixth crystallizer is controlled to be 22-28 °C below the saturation dissolution temperature.

[0027] Further, in the third step, from the first crystallizer to the last-stage crystallizer, stirring is required during the crystallization process, and the stirring speed is 200-800 rpm.

[0028] Further, in the fourth step, the ratio of ethanol and water in the washing solvent is the same as that in the crystallization solution, and the amount of the washing solvent used is 5%-15% of the mass of the ethyl maltol crystal.

[0029] Further, in the fourth step, the washed solvent is combined with a part of the crystallization mother liquor and used to dissolve the ethyl maltol crystallization raw material in the second step.

[0030] Further, in the fourth step, when the content of ethyl maltol in the filtered crystallization mother liquor is low, a part of the ethyl maltol crystallization mother liquor is recovered, the recovered solvent is used to dissolve the ethyl maltol crystallization raw material in the third step, and the recovered ethyl maltol and the ethyl maltol crude product are combined and used together as the raw material for vacuum distillation in the first step.

[0031] The present invention has the following advantages:

[0032] (1) The present invention provides a method for continuously purifying ethyl maltol by vacuum steam distillation - continuous vacuum distillation - continuous crystallization, realizing the continuous purification of ethyl maltol, with simple operation, reducing the contact between hot materials and air, effectively reducing the heat loss of ethyl maltol, and obtaining high-quality ethyl maltol products with good aroma; the primary crystallization yield of ethyl maltol is stably above 90%, and the purity is above 99.9%.

[0033] (2) The present invention uses vacuum steam distillation - vacuum distillation to replace the traditional sublimation, with simple operation and not easy to block the pipeline, greatly reducing the operation temperature, having good effects of removing odor, impurities and decoloring, low impurity content in the crystallization mother liquor, and the crystallization mother liquor and the washing solvent can be recycled and used to prepare the ethyl maltol solution to be crystallized, and the amount of the crystallization mother liquor that needs to be recovered is reduced by more than 80% compared with the traditional batch crystallization, realizing energy conservation and consumption reduction. Description of the Drawings

[0034] 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. For those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained by extending the provided drawings.

[0035] The structures, proportions, sizes, etc. illustrated 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 effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0036] Figure 1 A device for continuous purification of ethyl maltol provided by the present invention;

[0037] Figure 2 A schematic diagram of a vacuum steam distillation column provided by the present invention;

[0038] Figure 3 A schematic diagram of a vacuum ethyl maltol distillation column provided by the present invention;

[0039] Figure 4 A schematic diagram of a multi-stage crystallizer provided by the present invention. Specific embodiments

[0040] The following specific embodiments illustrate the embodiments 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 of them. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0041] A method for continuous purification of ethyl maltol, which is based on a purification device (as shown in the device Figure 1 shown) to perform purification operations. The device includes:

[0042] The system includes a vacuum distillation device, a dissolution device, a multi-stage crystallizer, and a post-treatment device connected in sequence; among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol; the outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and communicates with the dissolution device; the dissolution device is also provided with a discharge branch pipe, which is connected to the next-stage crystallizer, and the discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device;

[0043] The method includes:

[0044] Step 1: Continuously add the crude ethyl maltol into the vacuum distillation device, and perform vacuum steam distillation and vacuum ethyl maltol distillation in sequence to obtain the ethyl maltol crystallization raw material;

[0045] Step 2: The ethyl maltol crystallization raw material enters the dissolution device and dissolves in the mixed solution of ethanol and water to obtain the ethyl maltol solution to be crystallized after dissolution;

[0046] Step 3: The ethyl maltol solution to be crystallized enters the multi-stage crystallizer through the discharge branch pipe, start stirring, when the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the second crystallizer, start stirring, and the multi-stage crystallizer repeats this operation;

[0047] Step 4: The overflow liquid from the discharge branch pipe of the last-stage crystallizer enters the post-treatment device, and the ethyl maltol product is obtained through filtration, washing, and drying of the post-treatment device.

[0048] Further, the vacuum distillation device is a tower equipment, including a steam distillation tower (as shown in Figure 2 shown) and an ethyl maltol distillation tower (as shown in Figure 3 shown); the crude ethyl maltol is fed from the upper part of the steam distillation tower, and steam is fed from the lower part of the steam distillation tower. To ensure sufficient contact between the crude ethyl maltol and steam, the packing between the two feed ports has 10-20 theoretical plates.

[0049] Further, in Step 1, the addition ratio of deionized water is 3-5% of the mass of the crude ethyl maltol.

[0050] Further, in Step 1, in the vacuum steam distillation, the kettle temperature is maintained at 100-110 °C, and the pressure is 4-6 kPa; the temperature of the vacuum ethyl maltol distillation is 130-150 °C, and the pressure is 0.05-0.5 kPa.

[0051] Further, in Step 2, the mass ratio of ethyl maltol:ethanol:water is 1:(1-1.5):(0.5-1.5); the saturated dissolution temperature is 30-36 °C.

[0052] Further, in the second step, the temperature of the ethyl maltol solution to be crystallized is maintained at 5 - 10 °C above the saturation dissolution temperature.

[0053] Further, in the third step, the temperature in the first crystallizer is 1 - 3 °C below the saturation dissolution temperature; ethyl maltol is allowed to form crystal seeds under slow cooling; the total number of multi-stage crystallizers is 3 - 6 (as Figure 4 shown), the temperature in each stage of the crystallizer is 1 - 8 °C lower than the temperature in the previous stage of the crystallizer, and the temperature in the last stage of the crystallizer is 22 - 28 °C below the saturation dissolution temperature.

[0054] As an example, preferably, the temperature in the second crystallizer is 3 - 5 °C below the saturation dissolution temperature; when the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the third crystallizer, stirring is started, and the temperature in the third crystallizer is controlled at 5 - 10 °C below the saturation dissolution temperature;

[0055] When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the fourth crystallizer, stirring is started, and the temperature in the fourth crystallizer is controlled at 10 - 15 °C below the saturation dissolution temperature;

[0056] When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the fifth crystallizer, stirring is started, and the temperature in the fifth crystallizer is controlled at 15 - 21 °C below the saturation dissolution temperature;

[0057] When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the sixth crystallizer, stirring is started, and the temperature in the sixth crystallizer is controlled at 22 - 28 °C below the saturation dissolution temperature.

[0058] Further, in the third step, from the first crystallizer to the last stage of the crystallizer, stirring is required during the crystallization process, and the stirring speed is 200 - 800 rpm.

[0059] Further, in the fourth step, the ratio of the washing solvent to ethanol and water in the crystallization solution is the same, and the amount of the washing solvent used is 5% - 15% of the mass of the ethyl maltol crystals.

[0060] Further, in the fourth step, the washed solvent is combined with a part of the crystallization mother liquor and used to dissolve the ethyl maltol crystallization raw material in the second step.

[0061] Further, in the fourth step, when the content of ethyl maltol in the filtered crystallization mother liquor is low, a part of the ethyl maltol crystallization mother liquor is recovered, the recovered solvent is used to dissolve the ethyl maltol crystallization raw material in the third step, and the recovered ethyl maltol and the ethyl maltol crude product are combined and used together as the raw material for vacuum distillation in the first step.

[0062] Example 1

[0063] A method for continuous purification of ethyl maltol, which is based on a purification device for purification operations. The device includes:

[0064] The system includes a vacuum distillation device, a dissolution device, a multi-stage crystallizer, and a post-treatment device that are connected in sequence. Among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol. The outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and communicates with it. The dissolution device is also provided with a discharge branch pipe, which is connected to the next-stage crystallizer. The discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device;

[0065] The method includes:

[0066] Maintain the kettle temperature of the steam distillation tower (as shown in Figure 2 ) at 110 °C and the pressure at 6 kPa. The crude ethyl maltol (with a content of about 98.8%) is heated to 110 °C and fed from the upper part at a speed of 30 kg / min, and steam (5% of the mass of the crude ethyl maltol) is fed from the lower part. The two feed ports are separated by 10 theoretical plates. The low-boiling impurities with pungent odors in the crude ethyl maltol are removed by steam.

[0067] The material from which the low-boiling impurities have been removed is continuously fed into the ethyl maltol vacuum distillation tower. By adjusting the vacuum degree, the kettle temperature of the ethyl maltol distillation tower is maintained between 130 and 131 °C. Ethyl maltol is collected at the top of the tower at a speed of 29.4 kg / min as the crystallization raw material, and the bottom material of the tower kettle is intermittently pumped out by vacuum according to the liquid level as the high-boiling residue in the tower kettle.

[0068] The ethyl maltol crystallization raw material obtained by continuous vacuum steam distillation / continuous vacuum distillation is mixed with a certain proportion of ethanol and deionized water to form a crystallization solution to be crystallized. The ratio is ethyl maltol:ethanol:water mass ratio of 1:1:0.5, and its saturated dissolution temperature is between 35 and 36 °C. The prepared ethyl maltol solution is kept warm at 40 - 41 °C as the ethyl maltol crystallization solution to be crystallized for continuous crystallization.

[0069] The prepared ethyl maltol crystallization solution to be crystallized is added to the first crystallizer by overflow (see Appendix Figure 4 ), and the stirring is started. The first crystallizer (with a volume of 5 m 3, (with the same crystallizer volume below) The temperature is controlled by a jacket to maintain the temperature in the crystallizer at 33 - 34 °C, allowing ethyl maltol to grow slowly in the presence of crystal seeds. When the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the second crystallizer, and stirring is started to control the temperature in the second crystallizer at 31 - 32 °C. When the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the third crystallizer, and stirring is started to control the temperature in the third crystallizer at 27 - 28 °C. When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fourth crystallizer, and stirring is started to control the temperature in the fourth crystallizer at 23 - 24 °C. When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fifth crystallizer, and stirring is started to control the temperature in the fifth crystallizer at 17 - 18 °C. When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the sixth crystallizer, and stirring is started to control the temperature in the sixth crystallizer at 11 - 12 °C.

[0070] The total residence time of the ethyl maltol crystallization solution in the crystallizer is about 5.5 hours. The overflow liquid from the discharge branch pipe is collected, and ethyl maltol is separated from the mother liquor by filtration. The ethyl maltol collected per hour is washed with 80 kg of a cold ethanol - water mixed solution (ethanol - water mass ratio 1:0.5), dried to obtain the finished product. The finished product is 1620 kg per hour, and based on the feed amount, the crystallization yield is 91.0%. The purity of the finished product is detected to reach 99.95%, and it has a good aroma.

[0071] The washed solvent is collected separately. The content of ethyl maltol in the washing solvent is detected to reach 99.9%, and the content of ethyl maltol in the filtered mother liquor is detected to be 99.8%. The washing solvent and the filtered mother liquor are combined for the preparation of the subsequent ethyl maltol solution to be crystallized.

[0072] Example 2

[0073] A method for continuous purification of ethyl maltol, which is based on a purification device for purification operations. The device includes:

[0074] The system includes a vacuum distillation device, a dissolution device, a multi - stage crystallizer, and a post - treatment device connected in sequence; among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove the low - boiling impurities with pungent odors and the high - boiling impurities with darker colors in the ethyl maltol crude product; the outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and is in communication with the dissolution device; the dissolution device is also provided with a discharge branch pipe, which is connected to the next - level crystallizer, and the discharge branch pipe of the last - level crystallizer is connected to the post - treatment device;

[0075] The method includes:

[0076] Maintain the temperature of the still of the steam distillation column at 100 °C and the pressure at 4 kPa. The crude ethyl maltol (with a content of about 98.8%) is heated to 100 °C and fed from the upper part at a rate of 18 kg / min, and steam (3% of the mass of the crude ethyl maltol) is fed from the lower part. The two feed inlets are separated by 20 theoretical plates. Use steam to remove the low-boiling impurities with pungent odors in the crude ethyl maltol.

[0077] The material from which the low-boiling impurities have been removed continuously enters the vacuum distillation column for ethyl maltol. By adjusting the vacuum degree, the temperature of the still of the ethyl maltol distillation column is maintained between 149 and 150 °C. Ethyl maltol is collected at the top at a rate of 17.5 kg / min as the crystallization raw material, and the bottom material of the still is intermittently withdrawn by vacuum according to the liquid level as the high-boiling substances at the bottom of the still.

[0078] Mix the ethyl maltol crystallization raw material obtained by continuous vacuum steam distillation / continuous vacuum distillation with a certain proportion of ethanol and deionized water to prepare a solution to be crystallized. The ratio is ethyl maltol:ethanol:water mass ratio of 1:1.5:1.5, and its saturation dissolution temperature is between 31 and 32 °C. The prepared ethyl maltol solution is kept warm at 41 - 42 °C as the ethyl maltol solution to be crystallized for continuous crystallization.

[0079] Add the prepared ethyl maltol solution to be crystallized to the first crystallizer by overflow (see attachment Figure 4 ), and start stirring. The first crystallizer (with a volume of 5 m 3 , and the volumes of the following crystallizers are the same) is temperature-controlled by a jacket, and the temperature is controlled to maintain the temperature in the crystallizer at 28 - 29 °C, so that ethyl maltol slowly grows in the presence of crystal seeds. When the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the second crystallizer, start stirring, and control the temperature in the second crystallizer at 26 - 27 °C. When the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the third crystallizer, start stirring, and control the temperature in the third crystallizer at 21 - 22 °C. When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the fourth crystallizer, start stirring, and control the temperature in the fourth crystallizer at 16 - 17 °C. When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the fifth crystallizer, start stirring, and control the temperature in the fifth crystallizer at 10 - 11 °C. When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the sixth crystallizer, start stirring, and control the temperature in the sixth crystallizer at 3 - 4 °C.

[0080] The total residence time of the ethyl maltol crystallization solution in the crystallizer is about 5.5 hours. The overflow liquid from the discharge branch pipe is collected, and ethyl maltol is separated from the mother liquor by filtration. The ethyl maltol collected per hour is washed with 150 kg of a cold ethanol-water mixed solution (ethanol-water mass ratio 1:1), dried to obtain the finished product. The hourly output of the finished product is 980 kg. Based on the feed volume, the crystallization yield is 91.8%. The purity of the finished product is detected to reach 99.95%, and the aroma is good.

[0081] The washed solvent is collected separately. After detection, the content of ethyl maltol in the washing solvent reaches 99.9%. After detection, the content of ethyl maltol in the filtered mother liquor is 99.8%. The washing solvent and the filtered mother liquor are combined and used for the preparation of the subsequent ethyl maltol solution to be crystallized.

[0082] Example 3

[0083] A method for continuous purification of ethyl maltol, which is based on a purification device for purification operations. The device includes:

[0084] The system includes a vacuum distillation device, a dissolution device, a multi-stage crystallizer and a post-treatment device connected in sequence; among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol; the outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and communicates with the dissolution device; the dissolution device is also provided with a discharge branch pipe, which is connected to the next-stage crystallizer, and the discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device;

[0085] The method includes:

[0086] Maintain the kettle temperature of the steam distillation at 110 °C and the pressure at 6 kPa. Heat the crude ethyl maltol (content about 98.7%) to 110 °C and feed it from the upper part at a speed of 20 kg / min, and feed steam (4% of the mass of the crude ethyl maltol) from the lower part. The two feed ports are separated by 15 theoretical plates. Use steam to remove the low-boiling impurities with pungent odors in the crude ethyl maltol.

[0087] The material from which the low-boiling impurities have been removed continuously enters the ethyl maltol vacuum distillation column. By adjusting the vacuum degree, the kettle temperature of the ethyl maltol distillation column is maintained between 140 and 141 °C. Ethyl maltol is collected at the top of the column at a speed of 19.4 kg / min as the crystallization raw material, and the bottom material of the column is intermittently evacuated by vacuum according to the liquid level as the high-boiling residue in the column.

[0088] The ethyl maltol crystal raw material obtained by continuous reduced-pressure steam distillation / continuous reduced-pressure distillation is mixed with a certain proportion of ethanol and deionized water to prepare a solution to be crystallized. The ratio is ethyl maltol:ethanol:water mass ratio of 1:1:1.5, and its saturated dissolution temperature is 34 - 35 °C. The prepared ethyl maltol solution is kept warm at 40 - 41 °C and used as the ethyl maltol solution to be crystallized for continuous crystallization.

[0089] The prepared ethyl maltol solution to be crystallized is added to the first crystallizer by overflow (see attachment Figure 4 ), and the stirring is started. The first crystallizer (with a volume of 5 m 3 , and the volumes of the following crystallizers are the same) is temperature-controlled by a jacket, and the temperature is controlled to maintain the temperature in the crystallizer at 33 - 34 °C, so that ethyl maltol slowly grows in the presence of crystal seeds. When the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystal solution automatically overflows to the second crystallizer, and the stirring is started, and the temperature in the second crystallizer is controlled at 31 - 32 °C. When the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystal solution automatically overflows to the third crystallizer, and the stirring is started, and the temperature in the third crystallizer is controlled at 29 - 30 °C. When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystal solution automatically overflows to the fourth crystallizer, and the stirring is started, and the temperature in the fourth crystallizer is controlled at 24 - 25 °C. When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystal solution automatically overflows to the fifth crystallizer, and the stirring is started, and the temperature in the fifth crystallizer is controlled at 19 - 20 °C. When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystal solution automatically overflows to the sixth crystallizer, and the stirring is started, and the temperature in the sixth crystallizer is controlled at 12 - 13 °C.

[0090] The total residence time of the ethyl maltol crystal solution in the crystallizer is about 6 hours. The overflow liquid from the discharge branch pipe is collected, and ethyl maltol is separated from the mother liquor by filtration. The ethyl maltol collected per hour is washed with 60 kg of a cold ethanol-water mixed solution (ethanol-water mass ratio 1:1.5), dried to obtain the finished product. The finished product is 1080 kg per hour, and the crystallization yield is 91.2% based on the feed amount. The purity of the finished product is detected to reach 99.98%, and the aroma is good.

[0091] The washed solvent is collected separately. After detection, the content of ethyl maltol in the washing solvent reaches 99.9%, and all of it is used for preparing the ethyl maltol solution to be crystallized; after detection, the content of ethyl maltol in the filtered mother liquor is 99.1%. The washing solvent and a part of the filtered mother liquor are combined and used for the preparation of the subsequent ethyl maltol solution to be crystallized. Another part of the filtered mother liquor is used for recovery. The recovered ethanol is used for the preparation of the subsequent ethyl maltol solution to be crystallized. After the recovered ethyl maltol and the ethyl maltol crude product are combined, they are used together as the raw material for reduced-pressure distillation in step one.

[0092] Example 4

[0093] A method for continuous purification of ethyl maltol, which is based on a purification device for purification operations. The device includes:

[0094] The system includes a vacuum distillation device, a dissolution device, a multi-stage crystallizer, and a post-treatment device that are connected in sequence. Among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol. The outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and communicates with it. The dissolution device is also provided with a discharge branch pipe, which is connected to the next-stage crystallizer, and the discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device;

[0095] The method includes:

[0096] Maintain the kettle temperature of the steam distillation at 105 °C and the pressure at 5 kPa. After mixing the crude ethyl maltol and the recycled ethyl maltol (content about 98.7%), heat it to 105 °C and feed it from the upper part at a speed of 25 kg / min, and feed steam (5% of the mass of the crude ethyl maltol) from the lower part. The two feed ports are separated by 10 theoretical plates. Use steam to remove the low-boiling impurities with pungent odors in the crude ethyl maltol.

[0097] Continuously feed the material from which the low-boiling impurities have been removed into the ethyl maltol vacuum distillation column. By adjusting the vacuum degree, keep the kettle temperature of the ethyl maltol distillation column between 130 and 131 °C, and collect ethyl maltol at the top of the column at a speed of 24.2 kg / min as the crystallization raw material. The bottom material of the kettle is intermittently withdrawn by vacuum according to the liquid level as the kettle high-boiling substances.

[0098] Mix the ethyl maltol crystallization raw material obtained by continuous vacuum steam distillation / continuous vacuum distillation with a certain proportion of ethanol and deionized water to form a crystallization solution. The ratio is ethyl maltol:ethanol:water mass ratio of 1:1.5:0.5, and its saturated dissolution temperature is between 32 and 33 °C. The prepared ethyl maltol solution is kept warm at 38 - 39 °C as the ethyl maltol solution to be crystallized for continuous crystallization.

[0099] Add the prepared ethyl maltol solution to be crystallized to the first crystallizer by overflow (see attachment Figure 4 ), and start stirring. The first crystallizer (volume is 5 m 3, (with the same crystallizer volume as below) The temperature is controlled by a jacket to maintain the temperature in the crystallizer at 30 - 31 °C, allowing ethyl maltol to grow slowly in the presence of seeds. When the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the second crystallizer, and stirring is started, controlling the temperature in the second crystallizer at 28 - 29 °C. When the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the third crystallizer, and stirring is started, controlling the temperature in the third crystallizer at 24 - 25 °C. When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fourth crystallizer, and stirring is started, controlling the temperature in the fourth crystallizer at 20 - 21 °C. When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fifth crystallizer, and stirring is started, controlling the temperature in the fifth crystallizer at 14 - 15 °C. When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the sixth crystallizer, and stirring is started, controlling the temperature in the sixth crystallizer at 8 - 9 °C.

[0100] The total residence time of the ethyl maltol crystallization solution in the crystallizer is about 5.5 hours. The overflow liquid from the discharge branch pipe is collected, and ethyl maltol is separated from the mother liquor by filtration. The ethyl maltol collected per hour is washed with 130 kg of a cold ethanol - water mixed solution (ethanol - water mass ratio 1.5:0.5), dried to obtain the finished product. The finished product is 1350 kg per hour, and calculated based on the feed amount, the crystallization yield is 91.2%. The purity of the finished product is detected to reach 99.98%, and the aroma is good.

[0101] The washed solvent is collected separately. After detection, the content of ethyl maltol in the washing solvent reaches 99.9%, and all of it is used for preparing the ethyl maltol solution to be crystallized. After detection, the content of ethyl maltol in the filtered mother liquor is 99.1%. The washing solvent is combined with a part of the filtered mother liquor for preparing the subsequent ethyl maltol solution to be crystallized. Another part of the filtered mother liquor is used for recovery. The recovered ethanol is used for preparing the subsequent ethyl maltol solution to be crystallized. After the recovered ethyl maltol and the ethyl maltol crude product are combined, they are used together as the raw material for vacuum distillation in step one.

[0102] Example 5

[0103] A method for continuous purification of ethyl maltol, which performs purification operations based on a purification device. The device includes:

[0104] The system includes a vacuum distillation device, a dissolution device, a multi-stage crystallizer, and a post-treatment device that are connected in sequence. Among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol. The outlet end of the vacuum ethyl maltol distillation device is connected to and communicates with the dissolution device. The dissolution device is also provided with a discharge branch pipe, which is connected to the next-stage crystallizer, and the discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device.

[0105] The method includes:

[0106] Maintain the kettle temperature of the steam distillation column at 100 °C and the pressure at 4 kPa. After mixing the crude ethyl maltol and the recycled ethyl maltol (with a content of about 98.8%), heat it to 100 °C and feed it from the upper part at a speed of 24 kg / min, and feed steam (3% of the mass of the crude ethyl maltol) from the lower part. The two feed ports are separated by 20 theoretical plates. Use steam to remove the low-boiling impurities with pungent odors in the crude ethyl maltol.

[0107] Continuously feed the material from which the low-boiling impurities have been removed into the ethyl maltol vacuum distillation column. By adjusting the vacuum degree, keep the kettle temperature of the ethyl maltol distillation column between 149 and 150 °C. Collect ethyl maltol at the top of the column at a speed of 23.3 kg / min as the crystallization raw material, and intermittently draw the bottom material of the kettle through vacuum as the high-boiling residue in the kettle according to the liquid level.

[0108] Mix the ethyl maltol crystallization raw material obtained by continuous vacuum steam distillation / continuous vacuum distillation with a certain proportion of ethanol and deionized water to form a crystallization solution. The mixing ratio is ethyl maltol:ethanol:water = 1:1:1 by mass, and its saturated dissolution temperature is between 33 and 34 °C. Keep the prepared ethyl maltol solution at 38 - 39 °C for heat preservation as the ethyl maltol solution to be crystallized for continuous crystallization.

[0109] Overflow the prepared ethyl maltol solution to be crystallized into the first crystallizer (see Appendix Figure 4 ), and start stirring. The first crystallizer (with a volume of 5 m 3, (with the same crystallizer volume below), the temperature is controlled by a jacket to maintain the temperature in the crystallizer at 32 - 33 °C, enabling the slow growth of ethyl maltol in the presence of seed crystals. When the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the second crystallizer, and stirring is started to control the temperature in the second crystallizer at 30 - 31 °C. When the liquid level in the second crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the third crystallizer, and stirring is started to control the temperature in the third crystallizer at 28 - 29 °C. When the liquid level in the third crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fourth crystallizer, and stirring is started to control the temperature in the fourth crystallizer at 23 - 24 °C. When the liquid level in the fourth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the fifth crystallizer, and stirring is started to control the temperature in the fifth crystallizer at 18 - 19 °C. When the liquid level in the fifth crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows into the sixth crystallizer, and stirring is started to control the temperature in the sixth crystallizer at 11 - 12 °C.

[0110] The total residence time of the ethyl maltol crystallization solution in the crystallizer is about 5.5 hours. The overflow liquid from the discharge branch pipe is collected, and ethyl maltol is separated from the mother liquor by filtration. The ethyl maltol collected per hour is washed with 100 kg of a cold ethanol - water mixed solution (ethanol - water mass ratio 1:1), dried to obtain the finished product. The finished product obtained per hour is 1300 kg. Based on the feed amount, the crystallization yield is 91.4%. The purity of the finished product is detected to reach 99.98%, and the aroma is good.

[0111] The washed solvent is collected separately. After detection, the content of ethyl maltol in the washing solvent reaches 99.9%, and all of it is used for preparing the ethyl maltol crystallization solution to be crystallized. After detection, the content of ethyl maltol in the filtered mother liquor is 99.2%. The washing solvent is combined with a part of the filtered mother liquor for subsequent preparation of the ethyl maltol crystallization solution to be crystallized. Another part of the filtered mother liquor is used for recovery. The recovered ethanol is used for subsequent preparation of the ethyl maltol crystallization solution to be crystallized. After the recovered ethyl maltol and the ethyl maltol crude product are combined, they are used together as the raw material for vacuum distillation in Step 1.

[0112] Comparative Example 1

[0113] Using the method of Example 2 of Chinese Patent CN109513232B, crystallization operation is carried out using an evaporation crystallization device: white ethyl maltol crystal particles are obtained, with a purity of 98.3% and a crystallization yield of 90% based on the feed amount.

[0114] Comparative Example 2

[0115] In Example 1 of this patent, the temperature difference control of the continuous crystallization device is isothermal cooling, that is, the temperature in the first crystallizer is controlled at 31-32 °C, the temperature in the second crystallizer is controlled at 27-28 °C, the temperature in the third crystallizer is controlled at 23-24 °C, the temperature in the fourth crystallizer is controlled at 19-20 °C, the temperature in the fifth crystallizer is controlled at 15-16 °C, and the temperature in the sixth crystallizer is controlled at 11-12 °C. Other operating conditions are the same as those in Example 1. Finally, white ethyl maltol crystal particles are obtained, with a purity of 99.88% and a crystallization yield of 90% based on the feed rate.

[0116] In Comparative Example 1, only an evaporation crystallization device is used to purify the crude ethyl maltol, and the low-boiling and high-boiling impurities in the crude ethyl maltol cannot be effectively removed. Therefore, the purity of the obtained ethyl maltol is relatively low. In Comparative Example 2, instead of using a gradient cooling method, an isothermal cooling method is adopted. The supersaturation is relatively large in the early stage of crystallization, which may cause explosion nucleation and result in a small amount of impurities being wrapped, leading to a slight decrease in the purity of the ethyl maltol product.

[0117] 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 the present invention claimed.

Claims

1. A method for continuous purification of ethyl maltol, characterized in that, Purification operation is carried out based on a purification device, and the device includes: a vacuum distillation device, a dissolution device, a multi-stage crystallizer, and a post-treatment device that are connected in sequence; among them, the vacuum distillation device is divided into two parts, a vacuum steam distillation device and a vacuum ethyl maltol distillation device, which are used to remove low-boiling impurities with pungent odors and high-boiling impurities with darker colors in the crude ethyl maltol; the outlet end of the vacuum ethyl maltol distillation device is connected to the dissolution device and is communicated with the dissolution device; the dissolution device is also provided with a discharge branch pipe, which is connected to the subsequent multi-stage crystallizer, and the discharge branch pipe of the last-stage crystallizer is connected to the post-treatment device; The method includes: Step 1, continuously add the crude ethyl maltol into the vacuum distillation device, and carry out vacuum steam distillation and vacuum ethyl maltol distillation in sequence to obtain ethyl maltol crystallization raw materials; Step 2, the ethyl maltol crystallization raw materials enter the dissolution device and dissolve in a mixed solution of ethanol and water to obtain an ethyl maltol solution to be crystallized after dissolution; Step 3, the ethyl maltol solution to be crystallized enters the multi-stage crystallizer through the discharge branch pipe, start stirring, when the liquid level in the first crystallizer exceeds its discharge branch pipe, the crystallization solution automatically overflows to the second crystallizer, start stirring, and the multi-stage crystallizer repeats this operation; Step 4, the overflow liquid from the discharge branch pipe of the last-stage crystallizer enters the post-treatment device, and the ethyl maltol product is obtained through filtration, washing, and drying of the post-treatment device.

2. The method for continuous purification of ethyl maltol according to claim 1, characterized in that, The vacuum steam distillation device is a tower equipment, the crude ethyl maltol is fed from the upper part of the steam distillation tower, and the steam is fed from the lower part of the steam distillation tower. To ensure sufficient contact between the crude ethyl maltol and the steam, the packing between the two feed ports has 10 to 20 theoretical plates.

3. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the said Step 1, the addition ratio of deionized water is 3 to 5% of the mass of the crude ethyl maltol.

4. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the said Step 1, in the vacuum steam distillation, the kettle temperature is maintained at 100 to 110°C, and the pressure is 4 to 6 kPa; the temperature of the vacuum ethyl maltol distillation is 130 to 150°C, and the pressure is 0.05 to 0.5 kPa.

5. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the said Step 2, the mass ratio of ethyl maltol: ethanol: water is 1:(1 to 1.5):(0.5 to 1.5); the saturated dissolution temperature is 30 to 36°C; and the temperature of the ethyl maltol solution to be crystallized is maintained 5 to 10°C above the saturated dissolution temperature.

6. The method for continuous purification of ethyl maltol according to claim 1, wherein In the said Step 3, the total number of crystallizers is 3 to 6, and the temperature in the first-stage crystallizer is 1 to 3°C below the saturated dissolution temperature; the temperature in each stage of the crystallizer is 1 to 8°C lower than the temperature in the upper-stage crystallizer, and the temperature in the last-stage crystallizer is 22 to 28°C lower than the saturated dissolution temperature.

7. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the said Step 3, from the first-stage crystallizer to the last-stage crystallizer, stirring is required during the crystallization process, and the stirring speed is 200 to 800 rpm.

8. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the said Step 4, the ratio of the washing solvent to ethanol and water in the crystallization solution is the same, and the amount of the washing solvent used is 5% to 15% of the mass of the ethyl maltol crystals.

9. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the said Step 4, the washed solvent is combined with a part of the crystallization mother liquor and used to dissolve the ethyl maltol crystallization raw materials in Step 2.

10. A method for continuous purification of ethyl maltol according to claim 1, characterized in that, In the fourth step, when the content of ethyl maltol in the filtered crystallization mother liquor is low, part of the ethyl maltol crystallization mother liquor is recycled. The recycled solvent is used to dissolve the ethyl maltol crystallization raw material in the third step. After the recycled ethyl maltol and the crude ethyl maltol are combined, they are used together as the raw material for vacuum distillation in the first step.

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