Method for preparing dehydroacetic acid and sodium salt thereof through melt crystallization

Abstract

The invention discloses a method for preparing dehydroacetic acid and sodium salt thereof through melt crystallization, and belongs to the field of chemical engineering. The method comprises the following steps: 1, preparation of a crude dehydroacetic acid product: mixing crude ketene dimer, toluene, a catalyst and a polymerization inhibitor, reacting to prepare dehydroacetic acid, and cooling and crystallizing to obtain the dehydroacetic acid crude product; 2, melting, crystallizing and purifying a crude dehydroacetic acid product, namely heating and dissolving the prepared crude dehydroacetic acid product, conveying the crude dehydroacetic acid product into a melting crystallizer, carrying out gradient cooling crystallization, heating to dissolve most crystals, and heating to 109-115 DEG C to dissolve the product, so as to obtain a dehydroacetic acid crystal; and 3, neutralizing and crystallizing to prepare sodium dehydroacetate, namely feeding the obtained dehydroacetic acid crystals into a neutralization kettle, neutralizing with a 5% sodium hydroxide solution until the pH value is 8-12, then concentrating and crystallizing, and centrifuging to obtain a sodium dehydroacetate finished product.

Description

Technical Field

[0001] The present invention relates to a method for preparing dehydroacetic acid and its sodium salt by melt crystallization, belonging to the chemical industry field. Background Art

[0002] Dehydroacetic acid is an important chemical raw material. With the continuous development of biotechnology, the application of dehydroacetic acid in the biomedical field is becoming more and more extensive, and it can be used as an important raw material in aspects such as anti-tumor drugs, immunomodulators, and anti-infection drugs. In addition, in the fields of dyes and fragrances, dehydroacetic acid is also an important synthetic raw material. Therefore, the present invention has broad market prospects and application prospects.

[0003] Prior art: Toluene and refined diketene are used to carry out a condensation reaction under the catalysis of a catalyst, and then cooling crystallization is carried out in an enamel reaction kettle, and the finished product is packaged after drying. However, this method has a high cost and there is a problem of insufficient rectification yield, that is, the rectification yield is only 90%, a part of diketene is lost during the rectification process, and the rectification energy consumption is large; in order to solve this problem, in the prior art, crude diketene with a purity of 90% is also tried to directly replace refined diketene to prepare dehydroacetic acid under the action of a catalyst and an inhibitor, which reduces the raw material cost. However, the impurity content in the crude dehydroacetic acid produced by this method is relatively high and difficult to separate, resulting in a decline in the appearance and quality of the product. Although using crude diketene to prepare dehydroacetic acid in the prior art reduces the raw material cost, the impurity content in the crude dehydroacetic acid is relatively high and difficult to separate, resulting in a decline in the appearance and quality of the product. At the same time, in the prior art, an enamel reaction kettle is used to prepare dehydroacetic acid by the method of cooling crystallization, and the process energy consumption is large, which is not conducive to energy conservation and environmental protection. Therefore, a new technology is needed to solve these problems. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems in the prior art that the cost of preparing dehydroacetic acid from crude diketene is high, the impurity content of the product is high, and the appearance is black, sticky, with peculiar smell, etc., and thus a new process for preparing dehydroacetic acid and its sodium salt by melt crystallization is proposed. This process can improve the appearance and purity of the product, reduce the impurity content and peculiar smell, and also save energy.

[0005] The present invention provides a method for preparing dehydroacetic acid and its sodium salt by melt crystallization, comprising the following steps:

[0006] 1. Preparation of crude dehydroacetic acid: Mix crude diketene with toluene, a catalyst, and an inhibitor to react to prepare dehydroacetic acid. After the reaction ends, cooling crystallization is carried out to obtain crude dehydroacetic acid;

[0007] 2. Purification of crude dehydroacetic acid by melting crystallization: Heat the crude dehydroacetic acid obtained in Step 1 to 109 - 115°C for dissolution, then input it into a melting crystallizer in the fully dissolved state of the crude product, then carry out gradient cooling crystallization, then filter and discharge the mother liquor with a high impurity content into the mother liquor tank, then heat up to dissolve most of the crystals, discharge the sweat into the sweat tank, and then quickly heat up to 109 - 115°C at a rate of 15 - 55°C / h to dissolve the product, and discharge the product into the product tank to obtain dehydroacetic acid crystals;

[0008] 3. Preparation of sodium dehydroacetate by neutralization crystallization: Feed the dehydroacetic acid crystals obtained in Step 2 into a neutralization kettle, neutralize with 5% sodium hydroxide solution to a pH of 8 - 12, then carry out concentration crystallization, and then centrifuge to obtain the finished product of sodium dehydroacetate.

[0009] Further, the content of diketene in the crude diketene in Step 1 is 85 - 90%.

[0010] Further, the catalyst in Step 1 is triethylenediamine.

[0011] Further, the inhibitor in Step 1 is catechol.

[0012] Further, the mixing reaction in Step 1 means stirring at 45 - 85°C for 2.5 - 6.5 h.

[0013] Further, the mass ratio of crude diketene to toluene in Step 1 is 1 - 5:5 - 20.

[0014] Further, the mass ratio of crude diketene to catalyst in Step 1 is 1 - 5:0.005 - 0.03.

[0015] Further, the mass ratio of crude diketene to inhibitor in Step 1 is 1 - 5:0.006 - 0.035.

[0016] Further, the content of dehydroacetic acid in the crude dehydroacetic acid obtained in Step 1 is 78 - 80%.

[0017] Further, the gradient cooling in Step 2 means gradient cooling crystallization at a cooling rate of 1 - 15°C / h, cooling to 55 - 85°C, and then cooling to 35 - 55°C at a cooling rate of 1 - 35°C / h.

[0018] Further, the heating up in Step 2 means heating up uniformly at a heating rate of 1 - 55°C / h to 85 - 95°C, and then heating up at a heating rate of 1 - 10°C / h to 95 - 109°C.

[0019] Application of the method provided by the present invention in the field of preparation of dehydroacetic acid.

[0020] Compared with the prior art, the beneficial effects of the present technical solution are as follows:

[0021] 1. The present invention uses melt crystallization to prepare dehydroacetic acid, which can effectively reduce the impurity content and odor, and improve the appearance and quality of the product.

[0022] 2. In the present invention, crude diketene with a purity of 90% is used instead of refined diketene with a purity of 99% to prepare dehydroacetic acid, which reduces the raw material cost and improves the economic benefits.

[0023] 3. The present invention also omits the step of rectifying crude diketene with a purity of 90% to prepare refined diketene with a purity of 99%, which can save energy and meet the requirements of energy conservation and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart of preparing dehydroacetic acid by melt crystallization of the present invention.

[0025] Figure 2 It is a device flow chart of preparing dehydroacetic acid by melt crystallization of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] This embodiment provides a specific method for preparing dehydroacetic acid by melt crystallization. This method uses toluene as a solvent, and uses a catalyst and an inhibitor to prepare dehydroacetic acid from crude diketene. By using crude diketene instead of refined diketene, the raw material cost can be reduced and the economic benefits can be improved. The specific operation steps are as follows:

[0027] Example 1

[0028] 1. Preparation of crude dehydroacetic acid: Using toluene as a solvent, using the catalyst triethylenediamine and the inhibitor catechol, keeping the temperature at 45 °C for 2.5 h, preparing dehydroacetic acid from crude diketene with a content of about 90%. The mass ratio of crude diketene, toluene, catalyst, and inhibitor is 1:5:0.005:0.006. After the reaction is completed, the reaction solution is cooled and crystallized to obtain a crude dehydroacetic acid product with a content of 78%. The appearance of this crude product is poor, the color is brown, the crystal grain size is small, and it is easy to agglomerate.

[0029] 2. Purification of crude dehydroacetic acid by melt crystallization: Heat the crude dehydroacetic acid obtained in step 1 to 109°C, feed it into the melt crystallizer in a fully dissolved state, and then cool it to 35°C for crystallization (Programmed cooling I: The solution is cooled at a uniform rate of 1°C / h to 55°C, Programmed cooling II: Cool at a uniform rate of 1°C / h to 35°C, and the mother liquor is discharged into the mother liquor tank, with the mother liquor accounting for 0.2%). Filter to remove the mother liquor with a high impurity content, and then heat it to 95°C to dissolve most of the crystals (Sweating program I: The melt crystallizer is heated at a uniform rate of 1°C / h to 85°C, Sweating program II: Heat at a uniform rate of 1°C / h to 95°C, and the sweat is discharged into the mother liquor tank, with the sweat accounting for 0.3%). Finally, quickly heat it to 109°C at a rate of 15°C / h to dissolve the product, and then discharge the product into the product tank. Finally, dehydroacetic acid crystals with a content of 99.75% are obtained. The crystals have a good appearance, are white in color, have a relatively large crystal size, and have no peculiar smell.

[0030] 3. Preparation of sodium dehydroacetate by neutralization crystallization: Feed the dehydroacetic acid crystals obtained in step 2 into the neutralization kettle, neutralize the dehydroacetic acid crystals with a 5% sodium hydroxide solution, adjust the pH to about 8, concentrate, and after crystallization, perform centrifugation. Finally, a finished product of sodium dehydroacetate with a content of 99.90% is obtained. The finished product has a good appearance, is white in color, has a relatively large crystal size, and has no peculiar smell.

[0031] Example 2

[0032] 1. Preparation of crude dehydroacetic acid: Use toluene as a solvent, use the catalyst triethylenediamine and the inhibitor catechol, keep it warm at 55°C for 4h, and prepare crude diketene with a content of about 90% into dehydroacetic acid. The mass ratio of crude diketene, toluene, catalyst, and inhibitor is 2.5:13:0.02:0.02. After the reaction is completed, cool the reaction solution for crystallization to obtain crude dehydroacetic acid with a content of 79%. The crude product has a poor appearance, is brown in color, has a small crystal size, and is prone to caking.

[0033] 2. Purification of crude dehydroacetic acid by melt crystallization: Heat the crude dehydroacetic acid obtained in step 1 to 111°C. When it is in a completely dissolved state, pump it into a melt crystallizer, and then cool it crystallize step by step (Programmed cooling I: The solution is cooled at a uniform cooling rate of 10°C / h to 66°C, Programmed cooling II: Cool at a uniform cooling rate of 25°C / h to 50°C, and discharge the mother liquor into the mother liquor tank, with the mother liquor accounting for 32%). Filter to remove the mother liquor with a high impurity content, and then heat up to dissolve most of the crystals (Sweating program I: The melt crystallizer is heated at a uniform heating rate of 25°C / h to 91°C, Sweating program II: Heat at a uniform heating rate of 6°C / h to 105°C, and discharge the sweat into the mother liquor tank, with the sweat accounting for 21%). Finally, quickly heat up to 112°C at a rate of 35°C / h to dissolve the product, and then discharge the product into the product tank. Finally, dehydroacetic acid crystals with a content of 99.77% are obtained. The crystals have a good appearance, are white in color, have a relatively large crystal size, and have no peculiar smell.

[0034] 3. Preparation of sodium dehydroacetate by neutralization crystallization: Feed the dehydroacetic acid crystals obtained in step 2 into a neutralization kettle. Neutralize the dehydroacetic acid crystals with a 5% sodium hydroxide solution, adjust the pH to about 11, concentrate, and after crystallization, perform centrifugation. Finally, a finished product of sodium dehydroacetate with a content of 99.92% is obtained. The finished product has a good appearance, is white in color, has a relatively large crystal size, and has no peculiar smell.

[0035] Example 3

[0036] 1. Preparation of crude dehydroacetic acid: Use toluene as a solvent, use the catalyst triethylenediamine and the inhibitor catechol, keep it warm at 75°C for 5.5 h, and prepare crude diketene with a content of about 90% into dehydroacetic acid. The mass ratio of crude diketene, toluene, catalyst, and inhibitor is 2:10:0.02:0.015. After the reaction is completed, cool the reaction solution to crystallize to obtain crude dehydroacetic acid with a content of 78.5%. The crude product has a poor appearance, is brown in color, has a small crystal size, and is prone to caking.

[0037] 2. Purification of crude dehydroacetic acid by melt crystallization: The crude dehydroacetic acid obtained in step 1 is heated to 113°C, poured into a melt crystallizer in a fully dissolved state, and then crystallized by gradient cooling (programmed cooling I: the solution is uniformly cooled to 65°C at a cooling rate of 7°C / h, programmed cooling II: the solution is uniformly cooled to 40°C at a cooling rate of 20°C / h, and the mother liquor is discharged to the mother liquor tank, accounting for 15%), the mother liquor with high impurity content is filtered out, and then the temperature is raised to dissolve most of the crystals (Sweating procedure I: the melt crystallizer is heated to 90°C at a rate of 25°C / h, sweating procedure II: the temperature is heated to 100°C at a rate of 5°C / h, and the sweat is discharged into the mother liquor tank, and the sweat accounts for 20%). Finally, the temperature is quickly raised to 112°C at 20°C / h to dissolve the product, and then the product is discharged into the product tank, and finally dehydroacetic acid crystals with a content of 99.75% are obtained. The crystals have a good appearance, white color, large crystal size, and no odor.

[0038] 3. Preparation of sodium dehydroacetate by neutralization and crystallization: The dehydroacetic acid crystals obtained in step 2 are sent to a neutralization kettle, the dehydroacetic acid crystals are neutralized with a 5% sodium hydroxide solution, the pH is adjusted to about 10, and concentrated. After crystallization, centrifugation is performed to finally obtain a sodium dehydroacetate product with a content of 99.90%. The finished product has a good appearance, a white color, a large crystal size, and no odor.

[0039] Example 4

[0040] 1. Preparation of crude dehydroacetic acid: Toluene is used as solvent, triethylenediamine is used as catalyst, and catechol is used as inhibitor. The temperature is kept at 85°C for 6.5 hours to prepare dehydroacetic acid from crude diketone with a content of about 90%. The mass ratio of crude diketone, toluene, catalyst, and inhibitor is 5:20:0.03:0.035. After the reaction is completed, the reaction solution is cooled and crystallized to obtain a crude dehydroacetic acid with a content of 80%. The crude product has a poor appearance, a brown color, a small crystal size, and is easy to agglomerate.

[0041] 2. Purification of crude dehydroacetic acid by melt crystallization: Heat the crude dehydroacetic acid obtained in step 1 to 115°C, and feed it into the melt crystallizer in a fully dissolved state. Then, cool it down for crystallization in a gradient manner (Programmed cooling I: The solution is cooled uniformly at a cooling rate of 15°C / h to 85°C, Programmed cooling II: Cool uniformly at a cooling rate of 35°C / h to 54°C, and the mother liquor is discharged into the mother liquor tank, with the mother liquor accounting for 38%). Filter out the mother liquor with a high impurity content, and then heat it up to dissolve most of the crystals (Sweating program I: The melt crystallizer is heated uniformly at a heating rate of 55°C / h to 95°C, Sweating program II: Heat at a heating rate of 10°C / h to 109°C, and the sweat is discharged into the mother liquor tank, with the sweat accounting for 22%). Finally, quickly heat it up to 115°C at a rate of 55°C / h to dissolve the product, and then discharge the product into the product tank. Finally, dehydroacetic acid crystals with a content of 99.79% are obtained. The crystals have good appearance, are white in color, have relatively large crystal sizes, and have no peculiar smell.

[0042] 3. Preparation of sodium dehydroacetate by neutralization crystallization: Feed the dehydroacetic acid crystals obtained in step 2 into the neutralization kettle. Neutralize the dehydroacetic acid with a 5% sodium hydroxide solution, adjust the pH to about 12, concentrate it, and after crystallization, perform centrifugation. Finally, a finished product of sodium dehydroacetate with a content of 99.91% is obtained. The finished product has good appearance, is white in color, has relatively large crystal sizes, and has no peculiar smell.

[0043] Through the methods described in the above Examples 1 to 4, a finished product of sodium dehydroacetate with a purity as high as 99% can be obtained. Moreover, this method can reduce the raw material cost, improve the appearance and purity of the product, reduce the impurity content and peculiar smell, and at the same time save energy and reduce the process energy consumption.

[0044] Comparative Example 1

[0045] 1. Preparation of crude dehydroacetic acid: Use toluene as a solvent, use a catalyst and an inhibitor, keep it warm at 55°C for 4h, and prepare crude diketene with a content of about 90% into dehydroacetic acid. The mass ratio of crude diketene, toluene, catalyst, and inhibitor is 2.5:13:0.02:0.02. After the reaction is completed, cool the reaction solution for crystallization to obtain crude dehydroacetic acid with a content of 78.05%. The crude product is brown in color, has a strong peculiar smell, has small crystal sizes, and is relatively viscous and easy to agglomerate.

[0046] 2. Preparation of sodium dehydroacetate by neutralization crystallization: Feed the crude dehydroacetic acid obtained in step 1 into the neutralization kettle. Neutralize the dehydroacetic acid with a 5% sodium hydroxide solution, adjust the pH to about 11, concentrate it, and after crystallization, perform centrifugation. Finally, a finished product of sodium dehydroacetate with a content of 99.92% is obtained. The finished product is brown in color, has a strong peculiar smell, has small crystal sizes, and is relatively viscous and easy to agglomerate.

[0047] Comparative Example 2

[0048] Performed with reference to Example 4, wherein only the programmed cooling I in Step 2 was adjusted to cool at a uniform rate of 25 °C / h to 95 °C, and other steps and parameters remained unchanged. The final sodium dehydroacetate product obtained had a content of 99.32%. The product was brown in color, had a strong odor, small crystal grain size, was relatively viscous and prone to caking.

[0049] Comparative Example 3

[0050] Performed with reference to Example 4, wherein only the programmed cooling II in Step 2 was adjusted to cool at a uniform rate of 45 °C / h to 65 °C, and other steps and parameters remained unchanged. The final sodium dehydroacetate product obtained had a content of 99.19%. The product was brown in color, had a strong odor, small crystal grain size, was relatively viscous and prone to caking.

[0051] Comparative Example 4

[0052] Performed with reference to Example 4, wherein only the programmed sweating I in Step 2 was adjusted to heat at a uniform rate of 65 °C / h to 100 °C, and other steps and parameters remained unchanged. The final sodium dehydroacetate product obtained had a content of 99.02%. The product was brown in color, had a strong odor, small crystal grain size, was relatively viscous and prone to caking.

[0053] Comparative Example 5

[0054] Performed with reference to Example 4, wherein only the programmed sweating II in Step 2 was adjusted to heat at a uniform rate of 20 °C / h to 120 °C, and other steps and parameters remained unchanged. The final sodium dehydroacetate product obtained had a content of 99.51%. The product was brown in color, had a strong odor, small crystal grain size, was relatively viscous and prone to caking.

[0055] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit their execution order. Obvious improvements made by those skilled in the art to the present invention in combination with the existing common general knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing dehydroacetic acid and its sodium salt by melt crystallization, characterized in that, It includes the following steps: (1) Preparation of crude dehydroacetic acid: Mix crude diketene, toluene, a catalyst, and a polymerization inhibitor to react and prepare dehydroacetic acid. After the reaction ends, cool down and crystallize to obtain crude dehydroacetic acid; (2) Purify the crude dehydroacetic acid by melt crystallization: Heat the crude dehydroacetic acid obtained in step (1) to 109 - 115 °C for dissolution, then input it into a melt crystallizer in a completely dissolved state of the crude product, then perform gradient cooling crystallization, then filter and discharge the mother liquor with a high impurity content into the mother liquor tank, then heat up to 95 - 109 °C to dissolve most of the crystals, discharge the sweat into the sweat tank, and then quickly heat up to 109 - 115 °C at a rate of 15 - 55 °C / h to dissolve the product, and discharge the product into the product tank to obtain dehydroacetic acid crystals; (3) Prepare sodium dehydroacetate by neutralization crystallization: Feed the dehydroacetic acid crystals obtained in step (2) into a neutralization kettle, neutralize with a 5% sodium hydroxide solution to a pH of 8 - 12, then perform concentration crystallization, and then centrifuge to obtain the finished product of sodium dehydroacetate.

2. The method according to claim 1, characterized in that, In step (1), the content of diketene in the crude diketene is 85 - 90%.

3. The method according to claim 1, characterized in that, In step (1), the catalyst is triethylenediamine and the polymerization inhibitor is catechol.

4. The method according to claim 1, characterized in that, In step (1), the said mixing reaction means stirring at 45 - 85 °C for 2.5 - 6.5 h.

5. The method according to claim 1, characterized in that, In step (1), the mass ratio of the crude diketene to toluene is 1 - 5:5 - 20.

6. The method according to claim 1, characterized in that, In step (1), the mass ratio of the crude diketene to the catalyst is 1 - 5:0.005 - 0.

03.

7. The method according to claim 1, characterized in that, In step (1), the mass ratio of the crude diketene to the polymerization inhibitor is 1 - 5:0.006 - 0.

035.

8. The method according to claim 1, characterized in that, In step (2), the said gradient cooling means gradient cooling crystallization with a cooling rate of 1 - 15 °C / h, cooling to 55 - 85 °C, and then cooling at a cooling rate of 1 - 35 °C / h to 35 - 55 °C.

9. The method according to claim 1, characterized in that, In step (2), the said heating up means heating up uniformly at a heating rate of 1 - 55 °C / h to 85 - 95 °C, and then heating up at a heating rate of 1 - 10 °C / h to 95 - 109 °C.

10. Use of the method according to any one of claims 1 to 9 in the field of preparation of dehydroacetic acid.

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