A process for the preparation of ethyl acetoacetate by crude ester recycle cooling

Abstract

The application discloses a process method for preparing ethyl acetoacetate by crude ester circulation cooling, and belongs to the technical field of chemical industry. The method can dilute the heat generated in the reaction in time and effectively by performing crude ester circulation in the continuous reaction process, better solves the problem of heat accumulation in the reactor, and cannot dissipate heat in time, thereby causing the problem of rapid temperature rise, and avoids the "flying temperature" in the reaction process; the temperature in the reactor is stable without other complex and strict operation control, the operation is simple and feasible; the content of the crude product, the product quality and the yield are improved; the content of the crude methyl acetoacetate obtained by the method is 97.8-98.1%, the content of the finished product after rectification is 99.5-99.7%, and the product yield is 97.8-98.2%; the high-temperature resistance requirement of the pipeline equipment is reduced, and the safety hidden danger is reduced.

Description

Technical Field

[0001] This invention relates to a process for preparing ethyl acetoacetate by circulating cooling of crude ester, belonging to the field of chemical technology. Background Technology

[0002] Ethyl acetoacetate (EAA), also known as ethyl acetoacetate, is chemically named ethyl 3-oxobutyrate. It is a colorless liquid, slightly soluble in water and soluble in organic solvents. Ethyl acetoacetate is an important raw material for organic synthesis; it is a colorless or slightly yellow transparent liquid with a fruity aroma. It is used in the synthesis of dyes and pharmaceuticals and is also an important intermediate in other organic synthesis processes.

[0003] The traditional process for preparing ethyl acetoacetate involves dissolving ethanol and a catalyst completely, adding them to an esterification reactor, heating the reactor, and then adding diketene dropwise. After the addition is complete, the mixture is kept at a constant temperature and cooled to produce crude ethyl acetoacetate. The crude product is then distilled to obtain the final ethyl acetoacetate. However, this batch process has a long reaction time, and at higher temperatures, diketene is prone to self-polymerization, resulting in low yields and poor selectivity. Furthermore, from a safety perspective, this type of process poses significant safety risks.

[0004] There have been reports of using continuous flow reactors for the production of ethyl acetoacetate. However, the continuous flow reaction of ethyl acetoacetate has the following problems: (1) During continuous reaction, the heat inside the tube cannot be dissipated in time, which will cause heat accumulation and result in excessive heat inside the tube, making it impossible to effectively control the reaction temperature; (2) Diketene is prone to self-polymerization at high temperatures, so the reaction yield will decrease, and the heat accumulation poses a significant safety hazard. It also requires high temperature resistance of the pipeline equipment, which increases the cost of the equipment and pipeline.

[0005] To address this issue, CN 111039785A (A method for continuous production of methyl acetoacetate using a microchannel reactor) has been reported, employing a microchannel continuous flow reactor for the reaction. This method has the following advantages: (1) low equipment space occupancy, low production cost, and flexible production; (2) the microchannel reactor has miniaturized pipe size, a large specific surface area, and high mass and heat transfer characteristics. However, the reaction in the microchannel reactor still has the following problems: (1) it cannot completely solve the problem of rapid heat release and heat accumulation in the esterification reaction section, which causes a rapid temperature rise and is difficult to control stably in production; (2) special design of the microchannel structure is required to achieve the performance of an ideal plug flow reactor. Summary of the Invention

[0006] Therefore, this invention develops an apparatus and method for preparing ethyl acetoacetate. In this apparatus and method, the crude ethyl acetoacetate produced in a continuous flow reactor is cooled by a condenser and refluxed, then thoroughly mixed with the reaction substrate solution before being fed back into the continuous flow reactor for further reaction. In this invention, the crude ester mixing effectively dilutes the heat generated by the reaction, ensuring stable and controllable temperature within the reactor, suppressing side reactions, and improving product yield. The crude ester content is also higher than that of the previous continuous process. Furthermore, the apparatus and method of this invention only require the addition of crude ester reflux to a conventional continuous flow reactor, resulting in very low modification costs and suitability for industrial applications.

[0007] The first objective of this invention is to provide an apparatus for preparing ethyl acetoacetate. The apparatus includes an ethanol metering tank 1, a catalyst metering tank 2, an ethanol-catalyst mixing and storage tank 3, a diethylene storage tank 4, an esterification reactor 12, a condenser 10, a buffer tank 11, and a pressure regulating valve 13. The ethanol-catalyst mixing and storage tank 3 is connected to the ethanol metering tank 1 and the catalyst metering tank 2. The buffer tank 11 is connected to the downstream pipeline of the ethanol-catalyst mixing and storage tank 3 via a metering pump 9, allowing the crude ester in the buffer tank to be refluxed and mixed with the ethanol catalyst. The DK in the diethylene storage tank 4 is mixed again with the ethanol catalyst mixed with the crude ester via a metering pump 8 and then enters the esterification reactor 12 for reaction. The pressure regulating valve 13 controls the reaction pressure of the esterification reactor 12. The outlet of the esterification reactor 12 is connected to the condenser 10, and the downstream of the condenser is connected to the buffer tank 11.

[0008] In one embodiment of the present invention, the crude ester is refluxed as follows:

[0009] u (粗酯) :[u (醇) +u (DK) ]=(3~15):1, (u is the liquid flow rate, unit: kg / h)

[0010] In one embodiment of the present invention, the esterification reactor is a continuous flow reactor.

[0011] The second objective of this invention is to provide a process for preparing ethyl acetoacetate by circulating cooling of crude ester. This method involves cooling the crude ethyl acetoacetate obtained from the reaction using a condenser and then refluxing it back into the ethyl acetoacetate production process. Specifically, it includes:

[0012] (6) Inject ethanol and catalyst into the catalyst mixing section at a certain flow rate;

[0013] (7) Use a pump to pump the crude ester in the buffer tank out at a certain flow rate and reflux it, and mix it with the alcohol solution in the catalyst mixing section to obtain an alcohol-ester mixed solution.

[0014] (8) The solution of diketene (DK) and alcohol ester is fed into a continuous flow reactor at a certain flow rate to carry out the reaction;

[0015] (9) The crude ester produced in the continuous flow reactor is cooled by a condenser and then flows into a buffer tank;

[0016] (10) Part of the crude ester in the buffer tank is distilled to obtain the finished product, and the other part is refluxed and mixed with the alcohol solution in the catalyst mixing section.

[0017] In one embodiment, the crude ester is refluxed as follows:

[0018] u (粗酯) :[u (醇) +u (DK) ]=(3~15):1, (u is the liquid flow rate, unit: kg / h)

[0019] In one embodiment, the temperature range of the crude ester in the buffer tank is 30 to 65°C, and the initial temperature of diketene (DK) is -5°C to 15°C.

[0020] In one embodiment, the molar ratio of anhydrous ethanol to diketene is (1.01 to 1.08):1.

[0021] In one embodiment, the catalyst accounts for 0.05% to 0.35% of the total mass of the reactants (total mass of ethanol and diketene).

[0022] In one embodiment, the catalyst is selected from one or more of propylamine, butylamine, diethylamine, triethylamine, diethylenetriamine, aniline, and diisopropylamine.

[0023] In one embodiment, the reaction temperature ranges from 50 to 120°C; the residence time ranges from 20 to 60 minutes; and the reaction pressure ranges from 0.01 to 0.4 MPa.

[0024] In one embodiment, the continuous flow reactor can be any one of a series of reactors for continuous production, including microchannel reactors, tubular reactors, etc.

[0025] Advantages and effects of the present invention:

[0026] The method of this invention involves recycling the crude ester during a continuous reaction process.

[0027] (1) It can effectively dilute the heat generated by the reaction in a timely manner, and better solve the problem of heat accumulation in the reactor and the inability to dissipate heat in time, which causes the temperature to rise rapidly, thus avoiding "runaway temperature" in the reaction process.

[0028] (2) No other complex and strict operation and control are required to stabilize the temperature inside the reactor, and the operation is simple and feasible;

[0029] (3) The crude product content, product quality and yield are improved. The crude methyl acetoacetate content obtained by the method of the present invention is 97.8-98.1%, the content of the finished product after distillation is 99.5-99.7%, and the product yield is 97.8-98.2%.

[0030] (4) Only crude ester reflux needs to be added to the traditional continuous flow reactor, and the modification cost is very low, making it suitable for industrial applications.

[0031] (5) It reduces the high temperature resistance requirements for pipeline equipment and reduces safety hazards. Attached Figure Description

[0032] Figure 1 This is a diagram of a continuous reaction apparatus for ethyl acetoacetate. 1 is an ethanol metering tank, 2 is a catalyst metering tank, 3 is a catalyst mixing section, 4 is a diethylene (DK) storage tank, 5, 6, 7, 8, and 9 are metering pumps, 10 is a condenser, 11 is a buffer tank, 12 is an esterification reactor, and 13 is a pressure regulating valve. Detailed Implementation

[0033] Example 1

[0034] First, ethanol and catalyst are pumped into catalyst mixing section 3 from ethanol metering tank 1 and catalyst metering tank 2 respectively through metering pumps 5 and 6 at a certain flow rate. After mixing, metering pumps 7, 8, and 9 are started, and then diketene, alcohol solution, and crude ester in buffer tank are pumped in a certain flow rate. (粗酯) :[u (醇) +u (DK) The crude ester is fed into a continuous flow tubular esterification reactor 12 at a molar ratio of 12:1, with diketene and ethanol having a molar ratio of 1.06:1. The feed temperature of diketene is controlled at 11°C, the catalyst is triethylamine, and the amount of catalyst accounts for 0.2% of the total mass of the reactants. The reaction temperature is 100°C, the reaction residence time is 22 min, and the reaction pressure is adjusted to 0.18 MPa by the pressure regulating valve 13. After the reaction, the crude ester is cooled by the condenser 10 and then flows into the buffer tank 11, maintaining the temperature of the crude ester in the buffer tank at 50°C. Non-condensable gases are vented, and the crude ester in the buffer tank 11 is pumped into the distillation column by the metering pump for distillation.

[0035] Because the crude ester, cooled in a buffer tank, flows in, the heat generated by the reaction is effectively neutralized, preventing heat accumulation and ensuring stable and controllable temperatures in each section, thus minimizing requirements on piping and equipment. The crude ester obtained after the reaction has a content of 98.1%. After distillation, the product content is 99.7%, the product yield is 98.2%, and the acidity (calculated as acetic acid) is 0.017%.

[0036] Example 2: Apparatus for preparing ethyl acetoacetate

[0037] like Figure 1 The diagram shown is a schematic of a continuous reaction apparatus for ethyl acetoacetate.

[0038] The apparatus includes an ethanol metering tank 1, a catalyst metering tank 2, an ethanol-catalyst mixing and storage tank 3, a diethylene storage tank 4, an esterification reactor 12, a condenser 10, a buffer tank 11, and a pressure regulating valve 13. The ethanol-catalyst mixing and storage tank 3 is connected to the ethanol metering tank 1 and the catalyst metering tank 2. The buffer tank 11 is connected to the downstream pipeline of the ethanol-catalyst mixing and storage tank 3 via a metering pump 9, allowing the crude ester in the buffer tank to be refluxed and mixed with the ethanol catalyst. The DK in the diethylene storage tank 4 is mixed again with the ethanol catalyst mixed with the crude ester via a metering pump 8, and then enters the esterification reactor 12 for reaction. The pressure regulating valve 13 controls the reaction pressure of the esterification reactor 12. The reactants from the esterification reaction flow into the buffer tank 11 after passing through the condenser 10 to obtain crude methyl acetoacetate. The crude ester is then distilled to obtain the final product.

[0039] During the operation of the device, the crude ester reflux is controlled as follows: (粗酯) :[u (醇) +u (DK) ]=(3~15):1, (u is the liquid flow rate, unit: kg / h)

[0040] Example 3:

[0041] Compared to Example 1, the crude ester reflux ratio was adjusted to 3:1, while other processes and parameters remained the same. Specifically:

[0042] First, ethanol and catalyst are pumped into catalyst mixing section 3 from ethanol metering tank 1 and catalyst metering tank 2 respectively through metering pumps 5 and 6 at a certain flow rate. After mixing, metering pumps 7, 8, and 9 are started, and then diketene, alcohol solution, and crude ester in buffer tank are pumped in a certain flow rate. (粗酯) :[u (醇) +u (DK) The crude ester is fed into a continuous flow tubular esterification reactor 12 at a molar ratio of 3:1, with diketene and ethanol at 1.06:1. The feed temperature of diketene is controlled at 11°C, the catalyst is triethylamine, and the amount of catalyst accounts for 0.2% of the total mass of the reactants. The reaction temperature is 100°C, the reaction residence time is 22 min, and the reaction pressure is adjusted to 0.18 MPa by the pressure regulating valve 13. After the reaction, the crude ester is cooled by the condenser 10 and then flows into the buffer tank 11, maintaining the temperature of the crude ester in the buffer tank at 50°C. Non-condensable gases are vented, and the crude ester in the buffer tank is pumped into the distillation column by the metering pump for distillation.

[0043] After introducing the crude ester reflux process, the reaction temperature became relatively easier to control, with smaller fluctuations and greater stability. Testing revealed a decrease in the content of dehydroacetic acid and ethanol in the crude ester. The crude ester obtained after the reaction had a purity of 96.33%. After distillation, the product purity was 99.3%, the product yield was 93.4%, and the acidity (based on acetic acid) was 0.1%.

[0044] Comparative Example 1:

[0045] Compared to Example 1, there was no crude ester reflux, and other processes and parameters remained the same; specifically:

[0046] First, ethanol and catalyst are pumped into catalyst mixing section 3 at a certain flow rate from ethanol metering tank 1 and catalyst metering tank 2 via metering pumps 5 and 6, respectively. After mixing, metering pumps 7 and 8 are started to pump diketene and alcohol solution into continuous flow tubular esterification reactor 12. The molar ratio of diketene to ethanol is 1.06:1. The feed temperature of diketene is controlled at 11°C. The catalyst is triethylamine, and the amount of catalyst accounts for 0.2% of the total mass of reactants. The reaction temperature is 100°C, and the reaction residence time is 22 min. The reaction pressure is adjusted to 0.18 MPa via pressure regulating valve 13. After the reaction, the crude ester is cooled by condenser 10 and then flows into buffer tank 11. The temperature of the crude ester in the buffer tank is maintained at 50°C. Non-condensable gases are vented. The crude ester in buffer tank 11 is pumped into distillation column for distillation via metering pump.

[0047] Due to the intense exothermic reaction, the temperature was difficult to control stably, leading to localized heat accumulation and excessively high temperatures. This caused diketene to self-polymerize into dehydroacetic acid. Ethanol in certain areas of the esterification reactor easily vaporized, failing to fully react with diketene. Consequently, high levels of both ethanol and dehydroacetic acid were detected in the crude ester. Furthermore, prolonged heat accumulation can reduce reactor lifespan and increase the risk of "feed surge."

[0048] The crude ester obtained after the reaction had a content of 95.4%. After distillation, the crude ester had a product content of 99%, a product yield of 90.6%, and an acidity (calculated as acetic acid) of 0.17%.

[0049] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An apparatus for preparing ethyl acetoacetate, characterized in that, The apparatus includes an ethanol metering tank, a catalyst metering tank, an ethanol-catalyst mixing and storage tank, a diethylene storage tank, an esterification reactor, a condenser, a buffer tank, and a pressure regulating valve. The ethanol-catalyst mixing and storage tank is connected to both the ethanol metering tank and the catalyst metering tank. The buffer tank is connected to the downstream pipeline of the ethanol-catalyst mixing and storage tank via a metering pump, allowing the crude ester in the buffer tank to be refluxed and mixed with the ethanol catalyst. Diketene (DK) in the diethylene storage tank is mixed again with the ethanol catalyst containing the crude ester via the metering pump and then enters the esterification reactor for reaction. The pressure regulating valve controls the reaction pressure of the esterification reactor, and the outlet of the esterification reactor is connected to the condenser, with the buffer tank connected downstream of the condenser. During use, the crude ester reflux ratio of the device is controlled at u(crude ester):[u(alcohol) + u(DK)]=(3~15):1, where u is the liquid flow rate in kg / h.

2. A process for preparing ethyl acetoacetate by circulating cooling of crude ester, characterized in that, Using the apparatus of claim 1, the method involves refluxing the crude ethyl acetoacetate obtained from the reaction to the ethyl acetoacetate production process after cooling it in a condenser, and controlling the reflux ratio of crude ester u(crude ester):[u(alcohol) + u(DK)]=(3~15):1; where u is the liquid flow rate in kg / h.

3. The method according to claim 2, characterized in that, include: (1) Ethanol and catalyst are injected into the catalyst mixing section at a certain flow rate; (2) The crude ester in the buffer tank is pumped out and refluxed at a certain flow rate to be mixed with the alcohol solution in the catalyst mixing section to obtain an alcohol-ester mixed solution. (3) The diketene (DK) and alcohol ester mixture solution is fed into a continuous flow reactor at a certain flow rate to carry out the reaction; (4) The crude ester produced in the continuous flow reactor is cooled by a condenser and then flows into a buffer tank; (5) Part of the crude ester in the buffer tank is distilled to obtain the finished product, and the other part is refluxed and mixed with the alcohol solution in the catalyst mixing section.

4. The method according to claim 3, characterized in that, The temperature range of the crude ester in the buffer tank is 30 to 65°C, and the initial temperature of diketene (DK) is -5°C to 15°C.

5. The method according to claim 3, characterized in that, The molar ratio of ethanol to diketene is (1.01~1.08):

1.

6. The method according to claim 3, characterized in that, The catalyst accounts for 0.05% to 0.35% of the total mass of ethanol and diketene.

7. The method according to claim 3, characterized in that, The catalyst is selected from one or more of propylamine, butylamine, diethylamine, triethylamine, diethylenetriamine, aniline, and diisopropylamine.

8. The method according to claim 3, characterized in that, The continuous flow reactor includes any one of a microchannel reactor or a tubular reactor.

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