Acetoacetate rectification method and rectification system

Abstract

The invention discloses a rectification method and a rectification system for acetoacetic esters, and belongs to the technical field of chemical engineering. According to the method disclosed by the invention, a method of firstly removing high boilers and then removing low boilers is adopted, firstly, the high boilers in the crude ester are quickly removed at the initial stage of rectification, most high polymers such as tar are removed, side reactions caused by high polymer impurities in the subsequent rectification process are avoided, and then the low boilers are removed through rectification to obtain a finished product. According to the rectification mode, the residence time of the high-boiling residues is short, the treatment efficiency is higher, the yield and the purity of the acetoacetate crude ester prepared by taking the crude diketene as the raw material can be guaranteed or improved, the energy consumption is lower, the equipment is simpler, the occupied area is smaller, the investment is lower, and the method has the advantages that the materials are recycled, the energy consumption is saved and the production is safe; the method is suitable for industrial application.

Description

Technical Field

[0001] The present invention relates to a rectification method and a rectification system for acetoacetates, belonging to the field of chemical engineering technology. Background Art

[0002] Acetoacetates have numerous uses. Among them, methyl acetoacetate is an intermediate for fungicides hymexazol, dimethirimol, ethirimol, insecticides diazinon, coumaphos, pyrimidinoxon, herbicide imazethapyr, rodenticides warfarin, coumatetralyl, etc., used as a solvent for cellulose ethers and a component of a mixed solvent for cellulose resins, and also used in organic syntheses such as pesticides, pharmaceuticals, dyes, and polymer stabilizers; ethyl acetoacetate is an important organic synthesis raw material, a colorless or slightly yellow transparent liquid with a fruity fragrance, used for synthesizing dyes and drugs, and is also an important intermediate in other organic syntheses.

[0003] The preparation of acetoacetates (methyl acetoacetate or ethyl acetoacetate) is obtained by reacting high-quality diketene with alcohols (methanol or ethanol) to obtain crude diesters (methyl acetoacetate or ethyl acetoacetate), and then obtaining the finished product through rectification. High-quality diketene refers to diketene with a content greater than 97%, which can be obtained by rectification and purification of crude diketene through negative-pressure film evaporation. There are the following problems: (1) Crude diketene is very unstable when heated, prone to safety accidents during rectification, and the generated residues are also unstable and difficult to handle; (2) Crude diketene is also prone to polymerization during rectification, resulting in a low yield.

[0004] Therefore, some existing enterprises have switched to directly esterifying crude diketene with methanol to obtain crude methyl acetoacetate, reducing the rectification step of crude diketene, reducing energy consumption, improving process safety, and also reducing losses. For example, CN102276464A discloses a production method of methyl acetoacetate, in which crude diketene and methanol are subjected to an esterification reaction at 20 - 150°C, and the generated product is subjected to four-column negative-pressure continuous rectification to obtain methyl acetoacetate with a content greater than 99.7%. The negative-pressure continuous rectification is carried out in four columns: a low-boiling-point removal column, a medium-boiling-point removal column, a finished product column, and a high-boiling-point removal column; this process still has the following disadvantages: (1) large equipment investment and high rectification requirements; (2) there is still room for further improvement in the yield.

[0005] Therefore, it is necessary to improve the existing rectification method and system for acetoacetates. Summary of the Invention

[0006] In order to solve at least one of the above problems, the present invention has developed a rectification method and a rectification system for crude acetoacetates prepared from crude diketene, reducing equipment investment, lowering rectification requirements, and at the same time ensuring or increasing the yield of acetoacetate products.

[0007] In the previous R & D process, the inventor team found that in CN102276464A, methyl acetoacetate was directly produced by the reaction of crude diketene with methanol. However, since the crude diketene contains acetic anhydride and has strong acidity, the catalytic activity of the base catalyst is weakened, resulting in a slow reaction rate. At the same time, the content of crude diketene is low, and the crude ester directly produced has many impurities; in this invention, the methyl ester yield was increased by using a four-column distillation method. Its distillation system first removes low-boiling components and then produces the finished product, and then recovers part of the methyl ester from the high-boiling components, and the residue is sent for incineration treatment; however, such a distillation device and method will cause a long residence time of a large amount of high-boiling impurities such as tar in the entire distillation system, resulting in the easy ketolysis and acidolysis of methyl acetoacetate during distillation, generating acetone, formic acid, methyl acetate, etc., resulting in a decrease in the distillation yield and the quality of the finished product. The original distillation system can no longer meet the distillation requirements, so the distillation device needs to be improved.

[0008] Acid decomposition (part of methanol and acetic acid will further react to form methyl acetate):

[0009]

[0010] Ketonic decomposition:

[0011]

[0012] The present invention improves the traditional distillation system. In the improved distillation system, a method of first removing high-boiling components and then removing low-boiling components is used. First, a wiped-film evaporator is used. Under negative pressure conditions, the low- and medium-boiling materials in the crude ester are quickly evaporated and separated from the high-boiling polymer impurities and condensed and recovered. Subsequently, the low- and medium-boiling materials are distilled to obtain the finished product. Due to the high heat transfer efficiency and fast evaporation speed of the wiped-film evaporator, most of the high polymers such as tar are quickly removed in the wiped-film evaporator, greatly reducing the residence time of methyl acetoacetate with them and reducing the decomposition of methyl acetoacetate at high temperatures. At the same time, in the subsequent distillation stage of the present invention, compared with the traditional four-column distillation (CN102276464A), due to the reduction of high-boiling substances, the overall boiling point of the materials is reduced, and the temperatures required to remove low-boiling components and obtain the finished product are both reduced, which also has certain advantages in energy conservation and production safety. Moreover, the content of the discharge liquid of the low-boiling column and the bottom residue of the finished product column is higher than that of the crude ester prepared from crude diketene. Therefore, the materials other than the finished product can also be recycled back to the crude ester tank for recovery.

[0013] The first object of the present invention is to provide a rectification system for acetoacetates, comprising: a crude ester storage tank (1), a preheater (2), a wiped film evaporator (3), a low-boiling-point removal tower (4), a finished product rectification tower (8), and a finished product storage tank (9); wherein, the crude ester storage tank (1) is connected to the preheater (2) through a pipeline; the feed port pipeline of the wiped film evaporator (3) is connected to the preheater (2), and the discharge port of the wiped film evaporator (3) is connected to the low-boiling-point removal tower (4); the feed port of the finished product tower (8) is connected to the discharge port of the low-boiling-point removal tower (4) through a pipeline, and the liquid outlet of the finished product tower (8) is connected to the finished product storage tank (9).

[0014] In one embodiment, a residue discharge port is provided at the bottom of the wiped film evaporator (3). Optionally, the wiped film evaporator (3) includes a connecting pipe, an ear seat, a cylinder body, and an internal vacuum system.

[0015] In one embodiment, a feed port is provided in the middle of the tower body of the low-boiling-point removal tower (4). The feed port of the low-boiling-point removal tower (4) is connected to the discharge port of the wiped film evaporator (3) through a feed pipe, and the material is transported by a metering pump (14). A discharge port is provided at the bottom of the low-boiling-point removal tower (4).

[0016] In one embodiment, the low-boiling-point removal tower (4) includes a low-boiling-point removal tower body, packing, a stirrer, a thermometer, and a pressure gauge. A separator (6), a condenser (5), and a liquid outlet are provided at the upper part of the low-boiling-point removal tower (4), and the liquid outlet is connected to a head storage tank (7).

[0017] In one embodiment, a feed port is provided in the middle of the tower body of the finished product tower (8).

[0018] In one embodiment, a separator (6), a condenser (5), and a liquid outlet are provided at the upper part of the tower body of the finished product tower (8), and the liquid outlet is connected to the finished product storage tank (9).

[0019] In one embodiment, a liquid discharge port is provided at the bottom of the tower body of the finished product tower (8), which is directly connected to the crude ester storage tank.

[0020] In one embodiment, the finished product tower (8) includes a finished product tower body, packing, a stirrer, a thermometer, and a pressure gauge.

[0021] In one embodiment, the low-boiling-point removal tower (4) and the finished product tower (8) share a set of vacuum systems. Optionally, the vacuum system includes a vacuum buffer tank (10), a water ring vacuum pump (11), and a water-gas separator (12).

[0022] In one embodiment, the crude ester in the crude ester storage tank refers to crude methyl acetoacetate or crude ethyl acetoacetate prepared from crude diketene as a raw material.

[0023] In one embodiment, the rectification system is a system for rectifying crude esters of acetoacetic acid prepared from crude diketene as a raw material.

[0024] The present invention also provides a method for rectifying crude esters of acetoacetic acid. The method is to first treat the crude ester with a wiped film evaporator, and then successively carry out rectification in a de - low - boiling tower and a finished - product rectification tower to obtain methyl acetoacetate or ethyl acetoacetate.

[0025] In one embodiment, the crude ester is obtained by an esterification reaction of crude diketene and alcohols. Optionally, the esterification reaction is carried out at 20 - 150 °C.

[0026] In one embodiment, the treatment conditions of the wiped film evaporator are: the kettle temperature in the wiped film evaporator is 65 - 75 °C, and the vacuum degree is 0.096 - 0.099 MPa.

[0027] In one embodiment, before the crude ester enters the wiped film evaporator, it is pre - heated by a pre - heater, and the temperature of the pre - heater is 50 - 60 °C.

[0028] In one embodiment, the rectification conditions of the de - low - boiling tower are: the tower kettle temperature of the de - low - boiling tower is 90 - 100 °C, the vacuum degree is 0.093 - 0.097 MPa, and the reflux ratio is 8 - 12.

[0029] In one embodiment, the rectification conditions of the finished - product rectification tower are: the tower kettle temperature of the finished - product rectification tower is 95 - 100 °C, the vacuum degree is 0.095 - 0.098 MPa, and the reflux ratio is 0.1 - 0.2.

[0030] In one embodiment, the discharge from the de - low - boiling tower and the kettle liquid of the finished - product rectification tower are mixed with the raw material crude ester for recovery and recycling.

[0031] The present invention also provides a production method of esters of acetoacetic acid, comprising the following steps:

[0032] (1) Carry out an esterification reaction of crude diketene and alcohols at 20 - 150 °C to obtain crude esters of acetoacetic acid;

[0033] (2) Treat the crude ester obtained in step (1) with a wiped film evaporator first, and then successively carry out rectification in a de - low - boiling tower and a finished - product rectification tower to obtain methyl acetoacetate or ethyl acetoacetate.

[0034] In one embodiment, the purity of diketene in crude diketene is 90% - 95%.

[0035] In one embodiment, the crude diketene is a dimer obtained by the polymerization of ketene gas. However, ketene is relatively reactive and prone to self-polymerization. Therefore, most of the impurities in the crude diketene are polymers formed by the self-polymerization of ketene or diketene, and a part of the impurities are acetic acid, acetic anhydride, etc. The content of diketene in the crude diketene is 94-96%.

[0036] In one embodiment, the alcohol is methanol or ethanol.

[0037] In one embodiment, the molar ratio of the crude diketene to the alcohol is 1:1.1-1.3; the dosage of the catalyst is 0.4%-0.8% of the total weight of the reactants.

[0038] In one embodiment, the catalyst used in the esterification reaction is triethylamine.

[0039] Advantages of the present invention:

[0040] The present invention uses a method of first removing high-boiling components and then removing low-boiling components. First, the high-boiling components in the crude ester are quickly removed at the initial stage of rectification, removing most of the tar and other polymers, avoiding side reactions caused by polymer impurities in the subsequent rectification process, and then the low-boiling components are removed by rectification to obtain the finished product. In the rectification method of the present invention, the residence time of the high-boiling components is short and the treatment efficiency is higher. It can not only ensure or improve the yield and purity of the crude ester of acetoacetic ester prepared from crude diketene, but also the equipment is simpler, the floor area is smaller, and the investment is lower.

[0041] In addition, compared with the traditional four-column rectification (CN102276464A), the method of the present invention has advantages in energy conservation and production safety, and the content of the discharge liquid of the low-boiling column and the bottom residue of the finished product column is higher than that of the crude ester prepared from crude diketene. Therefore, the materials other than the finished product can also be recycled back to the large crude ester tank for recovery.

[0042] By quickly removing high-boiling components and then removing low-boiling components, the present invention avoids the decomposition of methyl acetoacetate caused by high-boiling impurities, making the rectification yield reach more than 96%. Finally, a finished product with a content greater than 99.8% is obtained, and the content of the finished product is also relatively high. Calculated based on an annual output of 40,000 t, for every 1% increase in the yield, the annual production capacity increases by about 400 t. The selling price of 1 t is about 8000 yuan, which can increase the net profit by 3,200,000 yuan / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the rectification method for acetoacetic esters.

[0044] Figure 2It is a schematic diagram of the rectification system for acetoacetate esters. Among them, 1 is the crude ester storage tank, 2 is the preheater, 3 is the wiped-film evaporator, 4 is the low-boiling-point removal tower, 5 is the condenser, 6 is the separator, 7 is the headstock tank, 8 is the finished product rectification tower, 9 is the finished product storage tank, 10 is the vacuum buffer tank, 11 is the water-ring vacuum pump, 12 is the water-gas separator, and 13, 14, and 15 are all metering pumps. Specific implementation mode

[0045] Yield of crude acetoacetate esters = (mass of crude acetoacetate esters prepared * content of crude esters) / (mass of crude diketene input * content of crude diketene)

[0046] Combined with Figure 1 , the rectification method of acetoacetate esters of the present invention will be described. The method is to first treat the crude ester prepared from crude diketene as the raw material in a wiped-film evaporator (kettle temperature is 65 - 75 °C, vacuum degree is 0.096 - 0.099 MPa), and then successively carry out rectification in a low-boiling-point removal tower (90 - 100 °C, vacuum degree is 0.093 - 0.097 MPa, reflux ratio is 8 - 12) and a finished product rectification tower (95 - 100 °C, vacuum degree is 0.095 - 0.098 MPa, reflux ratio is 0.1 - 0.2) to obtain methyl acetoacetate or ethyl acetoacetate. Further, the discharged liquid from the low-boiling-point tower and the bottom residue of the finished product tower can also be recycled back to the crude ester storage tank for recovery.

[0047] Example 1: Rectification method of crude methyl acetoacetate prepared from crude diketene as the raw material

[0048] (1) Preparation of crude methyl acetoacetate using crude diketene as the raw material:

[0049] Add 1216 Kg (38 Kmol) of methanol and 8.5 Kg of triethylamine as the catalyst to a 5000 L reaction kettle, stir and heat up to 55 °C, and start to dropwise add 3036 Kg (34.55 Kmol) of crude diketene with a content of 95.6%. The temperature rises gently to 110 °C, and the dropping time is 3.5 - 4 hours. After the dropping is completed, keep warm for 1 hour and the experiment is completed.

[0050] (2) Rectify the crude ester obtained in the previous step:

[0051] The crude ester obtained in the previous step is fed from the crude ester storage tank into a preheating kettle through a feed pump and heated. The temperature of the kettle is 55 - 60 °C. After preheating, it is pumped into a wiped-film evaporator for distillation separation. The temperature of the kettle in the wiped-film evaporator is 65 - 70 °C, and the vacuum degree is 0.097 - 0.098 MPa. Under these conditions, high-boiling residues are quickly separated. The material discharged from the wiped-film evaporator enters the middle part of the low-boiling-point removal tower, and under the conditions of a vacuum degree of 0.094 - 0.096 MPa and a kettle temperature of 95 - 98 °C, low-boiling substances such as methanol, acetone, acetic acid, and methyl acetate are removed by negative-pressure rectification. The bottom liquid in the low-boiling-point removal tower enters the middle part of the product tower. Under the conditions of a vacuum degree greater than 0.096 MPa and a kettle temperature of 95 - 98 °C, methyl acetoacetate product is obtained. The material discharged from the low-boiling-point removal tower and the bottom liquid of the product tower are recycled into the crude ester storage tank for cyclic rectification.

[0052] According to the method of this example, 3841.4 Kg of colorless and transparent ethyl acetoacetate product is obtained from the product tower, with a content of 99.82%, and the yield calculated based on diketene in the crude diketene is 96.02%.

[0053] Example 2: A rectification method for crude ethyl acetoacetate prepared from crude diketene as a raw material

[0054] Replace the methanol in Example 1 with ethanol to prepare crude ethyl acetoacetate and carry out rectification. Specifically:

[0055] (1) Prepare crude ethyl acetoacetate using crude diketene as a raw material:

[0056] Add 1840 Kg (40 Kmol) of ethanol and 10 Kg of triethylamine as a catalyst to a 5000 L reaction kettle. Stir and heat up to 70 °C, and start to dropwise add 3188 Kg (36.36 Kmol) of crude diketene with a content of 95.8%. The temperature slowly rises to 125 °C, and the dropping time is 3.5 - 4.5 hours. After the dropping is completed, keep it warm for 1.5 hours and the experiment is completed.

[0057] (2) Rectify the crude ester obtained in the previous step:

[0058] The crude ester obtained in the previous step is fed from the crude ester storage tank into a preheating kettle through a feed pump for heating. The temperature of the kettle is 55 - 60 °C. After preheating, it is pumped into a wiped film evaporator for distillation separation. The temperature of the kettle in the wiped film evaporator is 75 - 80 °C, and the vacuum degree is 0.096 - 0.098 MPa. Under these conditions, high-boiling residues are rapidly separated. The product from the wiped film evaporator enters the middle part of the low-boiling-point removal tower, and under the conditions of a vacuum degree of 0.093 - 0.096 MPa and a kettle temperature of 97 - 99 °C, low-boiling substances such as ethanol, acetone, acetic acid, and methyl acetate are removed by negative pressure rectification. The bottom liquid in the low-boiling-point removal tower enters the middle part of the product tower. Under the conditions of a vacuum degree greater than 0.096 MPa and a kettle temperature of 97 - 100 °C, ethyl acetoacetate product is obtained. The product from the low-boiling-point removal tower and the bottom liquid of the product tower are recycled into the crude ester storage tank for cyclic rectification.

[0059] According to the method of this embodiment, 4555 Kg of colorless and transparent ethyl acetoacetate product is obtained from the product tower, with a content of 99.84%. The yield calculated based on diketene in crude diketene is 96.21%.

[0060] Example 3: A rectification system for crude esters of acetoacetates prepared from crude diketene

[0061] As Figure 2 shown, it is a schematic diagram of the rectification system of the present invention. It includes: a crude ester storage tank (1), a preheater (2), a wiped film evaporator (3), a low-boiling-point removal tower (4), a product rectification tower (8), and a product storage tank (9); among them, the crude ester storage tank (1) is connected to the preheater (2) through a pipeline; the feed port pipeline of the wiped film evaporator (3) is connected to the preheater (2), and the discharge port of the wiped film evaporator (3) is connected to the low-boiling-point removal tower (4); the feed port of the product tower (8) is connected to the discharge port of the low-boiling-point removal tower (4) through a pipeline, and the liquid outlet of the product tower (8) is connected to the product storage tank (9).

[0062] Specifically, for the wiped film evaporator (3), the feed port pipeline is connected to the preheater (2), the discharge port is connected to the low-boiling-point removal tower, and a residue discharge port is provided at the bottom.

[0063] The low-boiling-point removal tower (4) includes a low-boiling-point removal tower body, packing, a stirrer, a thermometer, and a pressure gauge. A separator (6), a condenser (5), and a liquid outlet are provided at the upper part, and the liquid outlet is connected to a header storage tank (7). A feed port is provided in the middle of the tower body. The feed port is connected to a feed pipe, and the material is transported by a metering pump. A discharge port is provided at the bottom of the tower and is connected to a discharge pipe to the product tower.

[0064] The finished product tower (8) described above includes a finished product tower body, packing, a stirrer, a thermometer, and a pressure gauge. It is provided with a feed inlet in the middle, and the feed inlet is connected to the discharge outlet of the low-boiling-point tower by a pipeline; a separator (6), a condenser (5), and a liquid outlet are provided in the upper part, and the liquid outlet is connected to the finished product storage tank (9); a liquid discharge port is provided at the bottom of the tower body and is directly connected to the crude ester storage tank (1).

[0065] The low-boiling-point tower (4) and the finished product tower (8) share a set of vacuum systems. The vacuum system includes a vacuum buffer tank (10), a water ring vacuum pump (11), and a water-gas separator (12).

[0066] The working principle of the rectification system of the present invention:

[0067] First, the crude ester of acetoacetic ester prepared from crude diketene and methanol (or ethanol) as raw materials is pumped from the crude ester storage tank into a preheater for preheating, and then pumped into a wiped film evaporator for purification under reduced pressure to quickly remove high-boiling components. The residue is sent to incineration, and the remaining evaporated materials are pumped into the low-boiling-point tower by a pump for rectification under reduced pressure. Low-boiling components are discharged from the top of the tower. When the materials in the low-boiling-point tower reach the set height, the materials are transported to the finished product rectification tower for rectification under reduced pressure. The finished product ester is discharged from the top of the tower, and the bottom residue is sent to the crude ester storage tank.

[0068] Example 4:

[0069] 1152 Kg (36 Kmol) of methanol and 8 Kg of triethylamine as a catalyst are added to a 5000 L reaction kettle. The mixture is stirred and heated to 55 °C, and then 2872.9 Kg (32.73 Kmol) of crude diketene with a content of 95.7% is added dropwise. The temperature slowly rises to 110 °C, and the dropping time is 3.5 - 4 hours. After the dropping is completed, it is kept warm for 1 hour to complete the experiment.

[0070] The crude ester obtained in the previous step is pumped into a preheating kettle through a feed pump for heating. The kettle temperature is 55 - 60 °C. After preheating, it is pumped into a wiped film evaporator for distillation separation. The kettle temperature in the wiped film evaporator is 65 - 70 °C, and the vacuum degree is 0.097 - 0.098 MPa. Under these conditions, high-boiling residues are quickly removed; the discharged material from the wiped film evaporator enters the middle of the low-boiling-point tower, and under the conditions of a vacuum degree of 0.094 - 0.096 MPa and a kettle temperature of 95 - 98 °C, low-boiling substances such as methanol, acetone, acetic acid, and methyl acetate are removed by negative pressure rectification; the kettle liquid in the low-boiling-point tower enters the middle of the finished product tower, and under the conditions of a vacuum degree greater than 0.096 MPa and a kettle temperature of 95 - 98 °C, the product methyl acetoacetate is obtained. The discharged material from the low-boiling-point tower and the kettle liquid of the finished product tower are recycled into the crude ester storage tank for cyclic rectification.

[0071] According to the method of this example, 3649.7 Kg of colorless and transparent methyl acetoacetate product is obtained from the finished product tower, with a content of 99.80%, and the yield calculated based on diketene in the crude diketene is 96.05%.

[0072] Example 5:

[0073] Add 1184 Kg (37 Kmol) of methanol and 8.25 Kg of triethylamine as the catalyst into a 5000 L reactor. Stir and heat up to 55 °C, then start to dropwise add 2940.4 Kg (33.64 Kmol) of crude diketene with a content of 96.1%. The temperature slowly rises to 110 °C, and the dropping time is 3.5 - 4 hours. After the dropping is completed, keep the temperature for 1 hour and the experiment is over.

[0074] Feed the crude ester obtained in the previous step from the crude ester storage tank into the preheating kettle through a feed pump for heating. The kettle temperature is 55 - 60 °C. After preheating, it is fed into a wiped film evaporator for distillation separation. The kettle temperature in the wiped film evaporator is 65 - 70 °C, and the vacuum degree is 0.097 - 0.098 MPa. Under this condition, high-boiling residues are quickly separated. The product from the wiped film evaporator enters the middle part of the low-boiling removal tower, and under the conditions of a vacuum degree of 0.094 - 0.096 MPa and a kettle temperature of 95 - 98 °C, low-boiling substances such as methanol, acetone, acetic acid, and methyl acetate are removed by negative pressure rectification; the bottom liquid in the low-boiling removal tower enters the middle part of the product tower, and under the conditions of a vacuum degree greater than 0.096 MPa and a kettle temperature of 95 - 98 °C, methyl acetoacetate product is obtained. The product from the low-boiling removal tower and the bottom liquid of the product tower are recycled into the crude ester storage tank for cyclic rectification.

[0075] According to the method of this example, 3756.3 Kg of colorless and transparent methyl acetoacetate product is obtained from the product tower, with a content of 99.84%. The yield calculated based on diketene in the crude diketene is 96.12%.

[0076] Example 6:

[0077] Add 1932 Kg (42 Kmol) of ethanol and 10.6 Kg of triethylamine as the catalyst into a 5000 L reactor. Stir and heat up to 70 °C, then start to dropwise add 3360 Kg (38.2 Kmol) of crude diketene with a content of 95.5%. The temperature slowly rises to 125 °C, and the dropping time is 3.5 - 4.5 hours. After the dropping is completed, keep the temperature for 1.5 hours and the experiment is over.

[0078] The crude ester obtained in the previous step is fed from the crude ester storage tank into the preheating kettle through a feed pump and heated. The temperature of the kettle is 55 - 60 °C. After preheating, it is pumped into a wiped film evaporator for distillation separation. The temperature of the kettle in the wiped film evaporator is 75 - 80 °C, and the vacuum degree is 0.096 - 0.098 MPa. Under these conditions, the high-boiling residues are rapidly separated. The product from the wiped film evaporator enters the middle part of the low-boiling-point removal tower, and under the conditions of a vacuum degree of 0.093 - 0.096 MPa and a kettle temperature of 97 - 99 °C, low-boiling substances such as ethanol, acetone, acetic acid, and methyl acetate are removed by negative-pressure rectification. The bottom liquid in the low-boiling-point removal tower enters the middle part of the finished product tower. Under the conditions of a vacuum degree greater than 0.096 MPa and a kettle temperature of 97 - 100 °C, the product ethyl acetoacetate is obtained. The product from the low-boiling-point removal tower and the bottom liquid of the finished product tower are recycled into the crude ester storage tank for circulating rectification.

[0079] According to the method of this example, 4777.5 Kg of colorless and transparent ethyl acetoacetate product is obtained from the finished product tower, with a content of 99.81%. The yield calculated based on diketene in the crude diketene is 96.03%.

[0080] Comparative Example 1: The rectification system and rectification process in CN102276464A are adopted.

[0081] Using the same method as in Example 1, crude methyl acetoacetate is prepared from crude diketene: 1216 Kg (38 Kmol) of methanol and 8.5 Kg of triethylamine as a catalyst are added to a 5000 L reaction kettle. The mixture is stirred and heated to 55 °C, and then 3036 Kg (34.55 Kmol) of crude diketene with a content of 95.6% is added dropwise. The temperature rises gently to 110 °C, and the dropping time is 3.5 - 4 hours. After dropping, it is kept warm for 1 hour to complete the experiment.

[0082] The reaction product enters from the middle part of the low-boiling-point removal tower, and under the conditions of a vacuum degree of 0.08 - 0.09 MPa and a temperature of 70 - 100 °C, low-boiling substances such as methanol, acetone, and methyl acetate are removed by negative-pressure continuous rectification; the material in the low-boiling-point removal tower continuously enters the middle part of the medium-boiling-point removal tower, and under the conditions of a vacuum degree of 0.095 MPa, a temperature of 100 - 120 °C, and a reflux ratio greater than 12, higher-boiling substances such as acetic acid and acetic anhydride are removed by negative-pressure rectification; the material in the medium-boiling-point removal tower continuously enters, and under the conditions of a vacuum degree greater than 0.095 MPa and a temperature of 120 °C, the finished product methyl acetoacetate is obtained; the material in the bottom of the finished product tower continuously enters the bottom of the high-boiling-point removal tower, and under the conditions of a vacuum degree greater than 0.097 MPa and a temperature lower than 150 °C, high-waste substances are removed by negative-pressure rectification. At the same time, the product is recovered at the top of the tower, and the recovered product enters the reaction product for rectification. The high-boiling residues are discharged from the bottom of the high-boiling-point removal tower.

[0083] According to this method, 3779 Kg of colorless and transparent methyl acetoacetate product is obtained from the finished product tower, with a content of 99.8%. The yield calculated based on diketene in the crude diketene is 94.12%.

[0084] Comparative Example 2: Influence of the treatment conditions of the wiped-film evaporator

[0085] Compared with Example 1, only the following changes were made, and other steps and conditions were the same as those in Example 1:

[0086] Change the treatment process of the wiped-film evaporator to: the kettle temperature in the wiped-film evaporator is 77 - 80 °C, and the vacuum degree is 0.092 - 0.094 MPa.

[0087] According to this method, 3605.4 Kg of colorless and transparent methyl acetoacetate product was obtained in the finished product tower, with a content of 99.74%, and the yield calculated based on diketene in crude diketene was 94.73%.

[0088] Comparative Example 3: Influence of the treatment conditions of the wiped-film evaporator

[0089] Compared with Example 2, only the following changes were made, and other steps and conditions were the same as those in Example 2:

[0090] Change the treatment process of the wiped-film evaporator to: the kettle temperature in the wiped-film evaporator is 65 - 70 °C, and the vacuum degree is 0.093 - 0.095 MPa.

[0091] According to this method, 4287.3 Kg of colorless and transparent ethyl acetoacetate product was obtained in the finished product tower, with a content of 99.65%, and the yield calculated based on diketene in crude diketene was 95.12%.

[0092] The present invention has been disclosed by way of preferred embodiments, but it is not intended to limit the present invention. Any technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A rectification method for crude acetoacetate esters, characterized in that, The method is to first treat the crude ester with a wiped film evaporator, and then carry out rectification in a low-boiling-point removal tower and a finished product rectification tower successively to obtain methyl acetoacetate or ethyl acetoacetate; the crude ester is obtained by the esterification reaction of crude diketene and alcohols.

2. The rectification method according to claim 1, characterized in that, The treatment conditions of the wiped film evaporator are as follows: the preheated crude ester enters the wiped film evaporator, the kettle temperature in the wiped film evaporator is 65-75 °C, and the vacuum degree is 0.096-0.099 MPa.

3. The rectification method according to claim 1, characterized in that, The rectification conditions of the low-boiling-point removal tower are as follows: the tower kettle temperature of the low-boiling-point removal tower is 90-100 °C, the vacuum degree is 0.093-0.097 MPa, and the reflux ratio is 8-12.

4. The rectification method according to claim 1, characterized in that, The rectification conditions of the finished product rectification tower are as follows: the tower kettle temperature of the finished product rectification tower is 95-100 °C, the vacuum degree is 0.095-0.098 MPa, and the reflux ratio is 0.1-0.

2.

5. The rectification method according to claim 1, characterized in that, The discharge of the low-boiling-point removal tower and the kettle liquid of the finished product rectification tower are mixed with the raw material crude ester for recovery and recycling.

6. A production method for acetoacetate esters, characterized in that, It includes the following steps: (1). Carry out an esterification reaction on crude diketene and alcohols at 20-150 °C to obtain a crude ester of acetoacetate; (2). Rectify the crude ester obtained in step (1) by using the method described in any one of claims 1-5.

7. The production method according to claim 6, characterized in that, The molar ratio of the crude diketene to the alcohols is 1:1.1-1.3; the dosage of the catalyst is 0.4%-0.8% of the total weight of the reactants.

8. An acetoacetate ester rectification system, characterized in that, The acetoacetate rectification system includes: a crude ester storage tank (1), a preheater (2), a wiped film evaporator (3), a low-boiling-point removal tower (4), a finished product rectification tower (8), and a finished product storage tank (9); among them, the crude ester storage tank (1) is connected to the preheater (2) through a pipeline; the feed port pipeline of the wiped film evaporator (3) is connected to the preheater (2), and the discharge port of the wiped film evaporator (3) is connected to the low-boiling-point removal tower (4); the feed port of the finished product tower (8) is connected to the discharge port of the low-boiling-point removal tower (4) through a pipeline, and the liquid outlet of the finished product tower (8) is connected to the finished product storage tank (9).

9. The acetoacetate ester rectification system according to claim 8, characterized in that, The middle part of the tower body of the low-boiling-point removal tower (4) is provided with a feed port, the feed port of the low-boiling-point removal tower (4) is connected to the discharge port of the wiped film evaporator (3) through a feed pipe, the material is transported by a metering pump (14), and the bottom of the low-boiling-point removal tower (4) is provided with a discharge port; optionally, the discharge port of the low-boiling-point removal tower (4) is connected to the crude ester storage tank (1).

10. The acetoacetate ester rectification system according to claim 8, characterized in that, The bottom of the tower body of the finished product tower (8) is provided with a liquid discharge port, which is directly connected to the crude ester storage tank (1).

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