Method for recycling and preparing methyl acetoacetate

Abstract

The invention belongs to the field of chemical engineering, and particularly relates to a method for recycling and preparing methyl acetoacetate. The method comprises the following steps: mixing the tower kettle residual liquid of a crude product diethyl methyl ester finished product tower with methanol by taking methanol as an extracting agent, keeping the temperature, stirring, and standing for layering; and taking the upper-layer methyl diethyl ester methanol solution for rectification, and stopping discharging when the kettle temperature rises to 56-60 DEG C to finally obtain methyl diethyl ester. The content of the prepared and recovered diethyl methyl ester is 95.23 to 96.53 percent, and the molar recovery rate of the diethyl methyl ester is 82.99 to 88.21 percent through calculation. According to the method, the loss of the diethyl methyl ester is reduced, the recovery rate of the diethyl methyl ester and the quality of a finished product are improved, meanwhile, harmless treatment is carried out on the tower kettle raffinate, the environmental pollution is reduced, and the waste treatment cost is reduced for chemical enterprises.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry, and in particular relates to a method for recovering and preparing methyl acetoacetate. Background Art

[0002] Methyl acetoacetate (MAA), also known as diethyl methyl ester, has a molecular weight of 116 and a molecular formula of C5H8O3. It is a colorless liquid with a special odor, a density of 1.077, and a CAS of 105-45-3. It is an intermediate of commonly used fungicides such as mefenamic acid, dimethoate, and ethoxypyrimidine, insecticides such as diazinon, coumaphos, and pyrimethoxam, herbicides such as imidacloprid, and rodenticides such as coumaryl and warfarin. It can be used as a solvent for cellulose ether and a mixed solvent for cellulose resins, and can also be used in organic synthesis industries such as pesticides, medicines, dyes, and polymer stabilizers.

[0003] The commonly used industrial preparation method of methyl acetoacetate is mainly to purify the crude diketene to obtain the refined diketene, then react with methanol to obtain the crude diethyl methyl ester, and then obtain the finished product through distillation. However, since diketene is very unstable when heated, safety accidents are prone to occur during the distillation process, and the residues produced are also unstable and difficult to handle; and diketene is also prone to polymerization during the distillation process, resulting in a low yield of methyl acetoacetate.

[0004] At present, there is also a method of directly esterifying crude diketene with methanol to obtain crude methyl acetoacetate, and then distilling it to obtain the finished product. This improvement reduces the refining steps of crude diketene, reduces energy consumption, improves process safety, reduces losses, and optimizes the process flow. However, in the subsequent distillation process, the recovery rate of diethyl methyl ester from the finished product tower bottom residue is low, and the high temperature and high negative pressure in the tower also pose safety hazards. In addition, the residual liquid tower bottom discharge is a crystalline solid after cooling, which is not easy to transport. Therefore, the bottom residue is directly transported at high temperature during the production process, which puts higher requirements on the material and carrying capacity of the pipeline.

[0005] Since the crude diethyl methyl ester obtained by the reaction of crude diketene with methanol also carries a large amount of high-boiling substances in the crude diketene, these high-boiling substances exist in the residual liquid tower in the form of azeotropes with diethyl methyl ester, and the diethyl methyl ester therein cannot be recovered by simple distillation, resulting in the current low recovery rate of diethyl methyl ester. In addition, the recovered diethyl methyl ester carries part of the high-boiling substances back to the crude ester tank, and this cycle repeats, resulting in poor methyl ester separation effect in the finished product tower, low finished product content, and more diethyl methyl ester loss.

[0006] Patent CN102276464B provides a method for producing methyl acetoacetate, which uses crude diketene as a raw material, directly reacts with methanol in the presence of a catalyst to produce crude methyl acetoacetate, and uses a four-tower continuous distillation method to obtain the finished product methyl acetoacetate. However, there is not much exploration into the subsequent treatment of the diethyl methyl ester kettle residue.

[0007] Patent CN107986962A provides a method for recovering acetoacetate esters from acetoacetate ester distillation residues, using acetoacetate ester distillation residues as raw materials, using alcohols to react with dehydroacetic acid in the acetoacetate ester distillation residues and then removing them by distillation. However, in addition to physical distillation, chemical reactions are also involved, and the industrial process is relatively complicated.

[0008] Therefore, how to solve the problems of low yield of methyl acetoacetate, low recovery rate, high recovery conditions, complex industrial process and low safety in the subsequent residual liquid treatment process of crude diethyl methyl ester prepared from crude diketene is a common problem in the current chemical industry. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a method for recovering methyl acetoacetate, and the specific steps are as follows:

[0010] (1) Extraction:

[0011] Take the bottom liquid of the crude diethyl methyl ester finished product tower and mix it with methanol and let it stand;

[0012] Wherein, the preparation method of crude diethyl methyl ester finished product tower bottom liquid is:

[0013] The crude diketene with a purity of 90%-95% and methanol are subjected to an esterification reaction at 20-150° C. with 0.005%-0.05% of the total amount of the reactants being a tertiary amine, a compound containing ethyleneamine or a basic compound as a catalyst, and then the product generated by the esterification reaction is subjected to negative pressure continuous distillation in a distillation tower consisting of a low-boiling tower, a medium-boiling tower, a finished product tower and a high-boiling tower, and the negative pressure continuous distillation conditions are a vacuum degree of 0.08-0.10MPa and a temperature of 70-150° C. to obtain methyl acetoacetate; the remaining part in the distillation tower is the bottom residue of the crude diethyl methyl ester finished product tower;

[0014] Wherein, the tertiary amine is trimethylamine, triethylamine, or dimethyloctadecylamine; the compound containing ethyleneamine is diethylenetriamine, triethylenediamine, or tetraethylenediamine; the alkaline compound is sodium acetate, sodium methoxide, sodium ethoxide, or pyridine;

[0015] Among them, the low-boiling tower is a device used to separate low-boiling substances from a mixture; the medium-boiling tower is a distillation tower used to separate medium-boiling components; the high-boiling tower is a device used to separate high-boiling components, and the finished product tower is a distillation tower that separates and purifies the products after the reaction to finally obtain the desired products;

[0016] (2) Distillation:

[0017] After standing, take the upper diethyl methyl ester methanol solution for distillation. The distillation conditions are: adjust the kettle temperature to 32-40°C, the vacuum degree to 0.095-0.098Mpa, the reflux ratio to 8-12:1, and stop discharging when the kettle temperature rises to 55-65°C; finally, the tower bottom liquid is obtained, which is the recovered methyl acetoacetate product.

[0018] The results showed that the content of methyl acetoacetate in the recovered methyl acetoacetate product was 95.23-96.72%, and the molar recovery rate of diethyl methyl ester was calculated to be 82.99-88.21%.

[0019] Furthermore, the bottoms of the crude diethyl methyl ester finished tower in step (1) include 60% diethyl methyl ester and the rest are high-boiling substances.

[0020] Furthermore, the mass ratio of the crude diethyl methyl ester finished tower bottom residue to methanol in step (1) is 4-5:6-8.

[0021] Furthermore, the mixing conditions in step (1) are at 30-35° C., at a rotation speed of 200 rpm, and stirring for 3.0-4.5 h.

[0022] Furthermore, in step (1), the standing temperature is 30-35° C., and the standing time is 3.0-4.0 h.

[0023] Furthermore, it is characterized in that the kettle temperature is adjusted in step (2) preferably to 34-36°C.

[0024] Furthermore, the vacuum degree in step (2) is preferably 0.096-0.097 MPa.

[0025] Furthermore, the reflux ratio in step (2) is preferably 10:1.

[0026] Furthermore, in step (2), the discharge of the material is preferably stopped when the kettle temperature rises to 56-60°C.

[0027] Beneficial Effects

[0028] (1) The present invention recovers methyl acetoacetate by physical extraction throughout the process, and the process is simple and more suitable for industrialization.

[0029] (2) The boiling point difference between methanol and methyl acetoacetate used as the extractants of the present invention is large, and they are easier to separate. In the distillation process, increasing the reflux can reduce the methyl acetoacetate being taken out by methanol, which affects the yield.

[0030] (3) The extractant methanol used in the present invention can be recycled, further reducing the cost of recovering methyl acetoacetate.

[0031] (4) When separating methyl acetoacetate in the distillation section, the kettle temperature used in the present invention is 32° C.-65° C. and the vacuum degree is 0.095 MPa-0.098 MPa, which reduces the temperature and negative pressure conditions required for the distillation of methyl acetoacetate in the prior art, improves safety, and at the same time, the content of methyl acetoacetate in the recovered crude product is greater than 96%, and the recovery rate of methyl acetoacetate is 82.99%-87.7%, which is higher than the recovery rate of the residual liquid of direct high-temperature and high-pressure distillation, and has better effect.

[0032] (5) The diethyl methyl ester recovered by the present invention has a high content and a good recycling effect, and will not affect the subsequent crude ester recycling process, thereby reducing the loss of diethyl methyl ester.

[0033] (6) The raw material used in the present invention is the bottom liquid of the finished product tower. At the same time, the bottom liquid is treated, which reduces the amount of waste liquid discharged, reduces the cost of three wastes treatment, improves the economy of the entire production process, and is more suitable for industrialization.

[0034] (7) The method of the present invention separates and removes most of the high-boiling substances in the remaining layer while extracting and recovering diethyl methyl ester. Therefore, the diethyl methyl ester recovered by the method of the present invention hardly contains any high-boiling substances, and the finished diethyl methyl ester has a high purity of 95.23-96.72%. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0036] The test methods and calculation methods involved in the following embodiments are as follows:

[0037] 1. Analysis method of diethyl methyl ester content:

[0038] The analytical measurements were performed by gas chromatography.

[0039] 2. Methanol recovery method:

[0040] The top material obtained by distilling the extract is distilled and condensed to obtain methanol, and the purity of the recovered methanol is above 95%.

[0041] 3. Calculation method of methyl acetoacetate recovery rate:

[0042] Yield = (mass of recovered methyl acetoacetate × content of recovered methyl acetoacetate) ÷ (mass of residual liquid × content of methyl acetoacetate in residual liquid)

[0043] 4. Determination method of high boiling substances in the bottom liquid of crude diethyl methyl ester finished tower:

[0044] Since there is basically no low boiling point in the bottom residue of the raw material crude diethyl methyl ester finished product tower of the present invention, all substances except diethyl methyl ester are identified as high boiling substances, and the present invention uses a low boiling point extractant, that is, no new high boiling substances are introduced in the recovery process of methyl acetoacetate; therefore, the increase in the content of diethyl methyl ester in the subsequent distillation process means the reduction or removal of high boiling substances, and the method for determining the content of high boiling substances is as follows:

[0045] (1) Analysis by gas chromatography: Since it is difficult to measure high-boiling substances by gas chromatography, the kettle residue and the finished product diethyl methyl ester (content> 99.5%) are mixed in a certain proportion, and the mixed materials are put into the gas chromatograph for analysis to measure the diethyl methyl ester content after mixing;

[0046] (2) The content of diethyl methyl ester in the residual liquid is calculated by the formula: the content of diethyl methyl ester in the residual liquid = (the mass of diethyl methyl ester after mixing × the content of diethyl methyl ester after mixing - the mass of diethyl methyl ester in the finished product × the content of methyl ester in the finished product) / the mass of the residual liquid, and the content of diethyl methyl ester in the residual liquid is obtained. The remaining materials are all considered to be high-boiling substances, so the content of high-boiling substances = 1-the content of diethyl methyl ester in the residual liquid.

[0047] 5. Method for determining reflux ratio:

[0048] By controlling different reflux ratios for the distillation process and calculating and comparing the subsequent discharge content yield, it was finally determined that the reflux ratio used was 10:1.

[0049] Raw materials and equipment involved in the embodiments:

[0050] The steps for preparing the bottoms of the crude diethyl methyl ester finished product tower involved in the following embodiments can refer to the Chinese invention patent document with publication number CN102276464B, and the specific preparation method is as follows:

[0051] The crude diketene with a content of 91.3% is subjected to an esterification reaction with methanol at 20-150° C. using triethylamine as a catalyst, and then the product generated by the esterification reaction is subjected to negative pressure continuous distillation in a distillation tower, and the negative pressure continuous distillation conditions are a vacuum degree of 0.08-0.10 MPa and a temperature of 70-150° C. to obtain methyl acetoacetate; the remaining part in the distillation tower is the bottom residue of the crude diethyl methyl ester finished product tower;

[0052] Wherein, the tertiary amine is trimethylamine, triethylamine, or dimethyloctadecylamine; the compound containing ethyleneamine is diethylenetriamine, triethylenediamine, or tetraethylenediamine; the alkaline compound is sodium acetate, sodium methoxide, sodium ethoxide, or pyridine;

[0053] Among them, the low-boiling tower is a device used to separate low-boiling substances from a mixture; the medium-boiling tower is a distillation tower used to separate medium-boiling components; the high-boiling tower is a device used to separate high-boiling components, and the finished product tower is a distillation tower that separates and purifies the products after the reaction to finally obtain the desired products;

[0054] The above method is an embodiment of the present invention, and the preparation method of the bottom liquid of the crude diethyl methyl ester finished product tower is not limited thereto, and the specific implementation parameters can be adjusted as needed;

[0055] Preferably, the specific preparation method of the bottoms residue of the crude diethyl methyl ester finished product tower involved in the embodiment of the present invention is:

[0056] (1) Add 1280 kg (40 Kmol) of methanol, 3 kg of triethylenediamine and 1.5 kg of sodium acetate as catalysts to a 5000 L reactor, stir, and start dripping 3000 kg (33.25 Kmol) of crude diketene with a content of 93.1% at room temperature, and slowly increase the temperature to 115° C. The starting temperature to the final temperature range of dripping diketene can be 20 to 110° C. After dripping, continue to keep warm for 2 to 5 hours to complete the reaction;

[0057] (2) The reaction product enters the de-low boiling tower from the middle of the de-low boiling tower, and is continuously distilled under negative pressure at a vacuum degree of 0.08-0.09 MPa and a temperature of 70-100°C to remove low-boiling point substances such as methanol, acetone, and methyl acetate; the material in the de-low boiling tower continuously enters the middle of the de-medium boiling tower, and is continuously distilled under negative pressure at a vacuum degree of more than 0.095 MPa and a temperature of 100-120°C with a reflux ratio of more than 12 to remove higher boiling point substances such as acetic anhydride; The material continuously enters the middle of the finished product tower, and the product methyl acetoacetate is produced under the conditions of vacuum degree greater than 0.095Mpa and temperature between 100 and 120°C; the material in the kettle of the finished product tower continuously enters the bottom of the high-boiling removal tower, and the high-boiling substances are removed by negative pressure continuous distillation under the conditions of vacuum degree greater than 0.097Mpa and temperature below 150°C, and the product is recovered from the top of the tower, and the recovered product enters the reaction product for distillation, and the remaining part in the tower is the kettle residue of the crude diethyl methyl ester finished product tower.

[0058] In addition, the bottom liquid of the crude diethyl methyl ester finished product tower can also be directly taken from Nantong Acetic Acid Chemical Co., Ltd.; in this case, the bottom liquid of the crude diethyl methyl ester finished product tower includes 60% diethyl methyl ester and the rest is high-boiling substances.

[0059] The molecular formula and structural formula involved in the embodiments are:

[0060] The molecular formula of methyl acetoacetate involved in the following embodiments is: C5H8O3.

[0061] The structural formula of methyl acetoacetate involved in the following embodiments:

[0062]

[0063] Example 1: Preparation method for recovery of diethyl methyl ester

[0064] (1) Extraction:

[0065] Take 400 g of the crude diethyl methyl ester finished tower bottom residue and 600 g of methanol at 36°C and 200 rpm, stir for 4 h at 35°C and 200 rpm, then stand at 36°C for 3.0 h to wait for stratification;

[0066] (2) Distillation:

[0067] After standing, the upper layer of diethyl methyl ester methanol solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.096Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 60°C, the discharge was stopped, and finally 282.60g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0068] The results showed that the content of the recovered diethyl methyl ester was 96.72%, and the molar recovery rate of diethyl methyl ester was 85.4% after calculation.

[0069] Example 2: Preparation method for recovery of diethyl methyl ester

[0070] (1) Extraction:

[0071] Take 400 g of the crude diethyl methyl ester finished tower bottom residue and 800 g of methanol at 36°C and 200 rpm, stir for 3 h at 35°C and 200 rpm, then stand at 36°C for 3.5 h to wait for stratification;

[0072] (2) Distillation:

[0073] After standing, the upper layer of diethyl methyl ester methanol solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.096Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 58°C, the discharge was stopped, and finally 280.78g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0074] The results showed that the content of the recovered diethyl methyl ester was 95.23%, and the molar recovery rate of diethyl methyl ester was 83.56% after calculation.

[0075] Example 3: Preparation method for recovery of diethyl methyl ester

[0076] (1) Extraction:

[0077] Take 400 g of the crude diethyl methyl ester finished tower bottom residue and 700 g of methanol at 36°C and 220 rpm, stir for 4.5 h at 30°C and 200 rpm, then stand at 36°C for 4.0 h to wait for stratification;

[0078] (2) Distillation:

[0079] After standing, the upper layer of diethyl methyl ester methanol solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.097Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 56°C, the discharge was stopped, and finally 276.70g of the tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0080] The results showed that the content of the recovered diethyl methyl ester was 95.98%, and the molar recovery rate of diethyl methyl ester was 82.99% after calculation.

[0081] Example 4: Preparation method for recovery of diethyl methyl ester

[0082] (1) Extraction:

[0083] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of methanol at 36°C and 240 rpm, stir for 4.5 h at 30°C and 200 rpm, then stand at 36°C for 4.0 h to wait for stratification;

[0084] (2) Distillation:

[0085] After standing, the upper layer of diethyl methyl ester methanol solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.097Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 56°C, the discharge was stopped, and finally 273.21g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0086] The results showed that the content of the recovered diethyl methyl ester was 96.31%, and the molar recovery rate of diethyl methyl ester was 87.70% after calculation.

[0087] Example 5: Preparation method for recovery of diethyl methyl ester

[0088] (1) Extraction:

[0089] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of methanol at 36°C and 240 rpm, stir for 3.0 h at 30°C and 200 rpm, then stand at 36°C for 3.0 h to wait for stratification;

[0090] (2) Distillation:

[0091] After standing, the upper layer of diethyl methyl ester methanol solution was taken for distillation, the kettle temperature was adjusted to 42°C, the vacuum degree was 0.097Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 56°C, the discharge was stopped, and finally 274.14g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0092] The results showed that the content of the recovered diethyl methyl ester was 96.53%, and the molar recovery rate of diethyl methyl ester was 88.21% after calculation.

[0093] Example 6: Preparation method for recovery of diethyl methyl ester

[0094] Compared with Example 4, only the reflux ratio was adjusted:

[0095] (1) Extraction:

[0096] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of methanol at 36°C and 240 rpm, stir for 4.5 h at 30°C and 200 rpm, then stand at 36°C for 4.0 h to wait for stratification;

[0097] (2) Distillation:

[0098] After standing, the upper diethyl methyl ester methanol solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.097Mpa, and the reflux ratios were set to 8:1; 9:1; 11:1; 12:1, respectively. The kettle temperature was continuously raised by distillation, and the discharge was stopped when the kettle temperature rose to 56°C. The final bottom liquid amounts were 270.89g; 273.61g; 273.74g; 275.26g, respectively. The bottom liquid was the recovered diethyl methyl ester, and its content was analyzed. The results are shown in Table 1.

[0099] Table 1 Recovery results of diethyl methyl ester after adjusting the reflux ratio

[0100]

[0101] Comparative Example 1:

[0102] The specific implementation method is the same as that of Example 4, except that the extraction agent is changed to ethyl acetate:

[0103] (1) Extraction:

[0104] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of ethyl acetate at 36°C and 200 rpm, stir for 4.5 h at 30°C and 200 rpm, then let stand at 36°C for 4.0 h to wait for stratification;

[0105] (2) Distillation:

[0106] After standing, the upper layer of diethyl methyl ester ethyl acetate solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.097Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 56°C, the discharge was stopped, and finally 225.72g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0107] The results showed that the content of the recovered diethyl methyl ester was 90.23%, and the molar recovery rate of diethyl methyl ester was 67.89% after calculation.

[0108] Comparative Example 2

[0109] The specific implementation method is the same as that of Example 4, except that the extraction agent is changed to acetone:

[0110] (1) Extraction:

[0111] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of acetone at 36°C and 200 rpm, stir for 4.5 h at 30°C and 200 rpm, then let stand at 36°C for 4.0 h to wait for stratification;

[0112] (2) Distillation:

[0113] After standing, the upper layer of diethyl methyl ester acetone solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.097Mpa, the reflux ratio was 10:1, and the distillation caused the kettle temperature to rise continuously. When the kettle temperature rose to 56°C, the discharge was stopped, and finally 230.42g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0114] The results showed that the content of the recovered diethyl methyl ester was 91.23%, and the molar recovery rate of diethyl methyl ester was 70.07% after calculation.

[0115] Comparative Example 3

[0116] The specific implementation method is the same as that of Example 4, except that the extraction agent is changed to tetrahydrofuran:

[0117] (1) Extraction:

[0118] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of tetrahydrofuran at 36°C and 200 rpm, stir for 4.5 h at 30°C and 200 rpm, then stand at 36°C for 4.0 h to wait for stratification;

[0119] (2) Distillation:

[0120] After standing still, take the upper layer of tetrahydrofuran solution of diethyl methyl ester for distillation, adjust the kettle temperature to 40°C, the vacuum degree to 0.097Mpa, and the reflux ratio to 10:1. The distillation causes the kettle temperature to rise continuously. When the kettle temperature rises to 56°C, the discharge is stopped, and finally 203.07g of bottom liquid is obtained; the bottom liquid is the recovered diethyl methyl ester, and its content is analyzed.

[0121] The results showed that the content of the recovered diethyl methyl ester was 89.23%, and the molar recovery rate of diethyl methyl ester was 60.40% after calculation.

[0122] Comparative Example 4

[0123] The specific implementation is the same as in Example 4, except that the extraction agent is changed to ethanol:

[0124] (1) Extraction:

[0125] Take 500 g of the crude diethyl methyl ester finished tower bottom residue and 750 g of ethanol at 36°C and 200 rpm, stir for 4.5 h at 30°C and 200 rpm, then let stand at 36°C for 4.0 h to wait for stratification;

[0126] (2) Distillation:

[0127] After standing still, the upper layer of diethyl methyl ester ethanol solution was taken for distillation, the kettle temperature was adjusted to 40°C, the vacuum degree was 0.097Mpa, the reflux ratio was 10:1, and the kettle temperature was continuously raised by distillation. When the kettle temperature rose to 56°C, the discharge was stopped, and finally 220g of tower bottom liquid was obtained; the tower bottom liquid was the recovered diethyl methyl ester, and its content was analyzed.

[0128] The results showed that the content of the recovered diethyl methyl ester was 85.21%, and the molar recovery rate of diethyl methyl ester was 62.49% after calculation.

[0129] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for recovering methyl acetoacetate, characterized in that: The specific steps are as follows: (1) Extraction: Take the bottom liquid of the crude diethyl methyl ester finished product tower and mix it with methanol and let it stand; (2) Distillation: After standing, take the upper diethyl methyl ester methanol solution for distillation. The distillation conditions are: adjust the kettle temperature to 32-40°C, the vacuum degree to 0.095-0.098Mpa, the reflux ratio to 8-12:1, and stop discharging when the kettle temperature rises to 55-65°C; finally, the tower bottom liquid is obtained, which is the recovered methyl acetoacetate product.

2. The method according to claim 1, characterized in that In step (1), the bottom residue of the crude diethyl methyl ester finished tower comprises 60% diethyl methyl ester and the rest is high boiling substances; The preparation method of the bottom liquid of the crude diethyl methyl ester finished product tower is as follows: crude diketene with a purity of 90%-95% is mixed with methanol at 20-150° C., and at the same time, 0.005%-0.05% of the total amount of reactants of a tertiary amine, a compound containing ethyleneamine or a basic compound is added as a catalyst to carry out an esterification reaction, and then the product generated by the esterification reaction is subjected to negative pressure continuous distillation in a distillation tower, and the negative pressure continuous distillation conditions are a vacuum degree of 0.08-0.10MPa and a temperature of 70-150° C. to obtain methyl acetoacetate; the remaining part in the distillation tower is the bottom liquid of the crude diethyl methyl ester finished product tower; Wherein, the tertiary amine refers to trimethylamine, triethylamine, or dimethyloctadecylamine; the compound containing ethyleneamine is diethylenetriamine, triethylenediamine, or tetraethylenediamine; and the alkaline compound refers to sodium acetate, sodium methoxide, sodium ethoxide, or pyridine.

3. The method according to claim 1, characterized in that The mass ratio of the crude diethyl methyl ester finished tower bottom residue to methanol in step (1) is 4-5:6-8.

4. The method according to claim 1, characterized in that The mixing conditions in step (1) are at 30-35° C., at a rotation speed of 200 rpm, and stirring for 3.0-4.5 h.

5. The method according to claim 1, characterized in that The standing temperature in step (1) is 30-35° C., and the standing time is 3.0-4.0 h.

6. The method according to claim 1, characterized in that The kettle temperature in step (2) is preferably adjusted to 34-36°C.

7. The method according to claim 1, characterized in that The vacuum degree in step (2) is preferably 0.096-0.097 MPa.

8. The method according to claim 1, characterized in that The reflux ratio in step (2) is preferably 10:

1.

9. The method according to claim 1, characterized in that: In step (2), the discharge of the material is stopped when the kettle temperature rises to 56-60°C.

10. A finished product of methyl acetoacetate recovered by the method of any one of claims 1 to 9, characterized in that: The content of methyl acetoacetate in the methyl acetoacetate finished product is 95.23-96.72%, and the molar recovery rate of methyl acetoacetate is 82.99-88.21%.

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