A method for preparing methyl acetoacetate

Abstract

The invention discloses a method for preparing methyl acetoacetate, and belongs to the field of chemical technology. The method of the invention comprises the following steps: firstly injecting methanol and a catalyst at a certain flow rate respectively, then using a pump to pump out the crude ester in a buffer tank at a certain flow rate, mixing it with an alcohol solution, and then injecting the diketene and alcohol ester mixed solution into a continuous flow reactor at a certain flow rate for reaction. The method of the invention circulates the crude ester during the continuous reaction process, which can timely and effectively dilute the heat generated by the reaction, and better solves the problem of heat accumulation in the reactor, inability to dissipate heat in time, and thus causing a rapid rise in temperature, reduces safety hazards, improves product quality and yield, and reduces the requirements for the temperature resistance of pipeline equipment.

Description

Technical Field

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

[0002] Methyl acetoacetate, also known as diethyl methyl ester, has the chemical name 3-methyl ketobutyrate.

[0003] English name: Methyl acetoacetate

[0004] Appearance: Colorless liquid

[0005] Solubility: easily soluble in water, 460g / L (20℃)

[0006] CAS No.:105-45-3

[0007] Molecular formula:C5H8O3

[0008] Structural formula:

[0009]

[0010] Molecular weight: 116

[0011] Melting point(℃):-28℃

[0012] Relative density (water = 1): 1.077

[0013] Function and use: Methyl acetoacetate is an intermediate of fungicides such as mefenamic acid, dimethoate, and pyrimidine, insecticides such as diazinon, coumaphos, and pyrimidin, herbicides such as imidacloprid, rodenticides such as coumarol and warfarin, etc. It is used as a solvent for cellulose ether and a component of a mixed solvent for cellulose resins. It is also used in organic synthesis of pesticides, medicines, dyes, polymer stabilizers, etc.

[0014] The traditional preparation process of methyl acetoacetate: methanol and catalyst are fully dissolved and added to the esterification reactor, diketene is added dropwise at a high temperature, and after the addition is completed, the mixture is cooled and kept warm to generate crude methyl acetoacetate, which is then distilled to obtain the finished methyl acetoacetate. Due to the long reaction time of the intermittent process, diketene is very likely to self-polymerize at a high temperature, resulting in a low reaction yield and poor selectivity. From a safety perspective, this type of process has a high safety risk.

[0015] In recent years, the research work on flow, mixing, reaction and other aspects related to continuous flow reactors has developed rapidly, driving the rapid development of continuous reactor technology. Continuous flow reactors can greatly improve heat and mass transfer, strengthen reaction and heat exchange effects, and at the same time, because they can achieve precise control of process conditions such as material ratio and reaction temperature, chemical reactions can be carried out with precise ratio, strict temperature control, high selectivity, green and safe, and also provide a practical solution to many problems in traditional intermittent production processes.

[0016] Since the heat in the tube cannot be diffused in time when methyl acetoacetate reacts continuously in the continuous flow reactor, heat accumulation will cause excessive heat in the tube, and the reaction temperature cannot be effectively controlled. Diketene is easy to self-polymerize at high temperatures, so the reaction yield will decrease, and heat accumulation poses a great safety hazard. It also requires high high temperature resistance of pipeline equipment, which increases the cost of equipment and pipelines.

[0017] Existing technology processing technology:

[0018] (1) Liu Jianwu, Jiang Han, Yan Shenghu, Zhang Yue, Shen Jiefa, Gu Shunlin, Ma Xiaoming, Chen Daixiang. A method for continuous production of methyl acetoacetate using a microchannel reactor. Changzhou: CN 111039785A, 2020.04.21.

[0019] The reaction is carried out using a microchannel continuous flow reactor. The microchannel reactor requires a special design of the microchannel structure. Although the microchannel reactor has miniaturized pipe size, large specific surface area and high mass transfer and heat transfer characteristics, it still cannot completely solve the problem of heat accumulation in the esterification reaction section due to the violent reaction and too fast release of reaction heat, which causes the temperature to rise rapidly, and it is difficult to stably control it in production. Summary of the invention

[0020] In order to solve at least one of the above problems, the present invention has developed a process for preparing methyl acetoacetate by circulating cooling of crude ester, which is a process method that can effectively dissipate heat and control temperature during the continuous reaction of methyl acetoacetate, making the continuous esterification reaction safer, the equipment pipeline has low high temperature resistance requirements, and the reaction yield is higher; at the same time, there is no need to significantly transform the existing production equipment, which is suitable for industrial application. Specifically, it includes: methanol and catalyst are respectively pumped into the storage tank at a certain ratio of flow rate (catalyst mixing section), and then the crude ester in the buffer tank is pumped out at a certain flow rate by a pump, mixed with an alcohol solution, and then diketene (DK) and the alcohol ester mixed solution are pumped into a continuous flow reactor at a certain flow rate for reaction, and the crude ester after the reaction flows through the condenser to cool down, and then flows into the buffer tank. Due to the circulation of crude ester, the process method can timely and effectively dilute the heat generated by the reaction, and the temperature in the reactor can be stabilized without other complex and strict operation control. The operation is simple and feasible, avoiding "flying temperature" during the reaction process, improving the product yield, and the crude ester content obtained is also improved, reducing the high temperature resistance requirements for pipeline equipment, and reducing safety hazards.

[0021] The invention mainly aims at the problem that the reaction heat generated in the continuous reaction process of methyl acetoacetate cannot be diffused in time, resulting in temperature runaway, and develops a process method for preparing methyl acetoacetate by circulating cooling of crude ester.

[0022] The reaction formula for producing methyl acetoacetate is as follows:

[0023]

[0024] The process is as follows:

[0025] In one embodiment, the crude ester reflux ratio is as follows:

[0026] u (粗酯) : [u (醇) +u (DK) ]=(3~15):1

[0027] (u is the liquid flow rate, unit: kg / h)

[0028] In one embodiment, the crude ester temperature in the buffer tank ranges from 30°C to 65°C, and the initial temperature of DK ranges from -5°C to 15°C.

[0029] In one embodiment, the molar ratio of anhydrous methanol to diketene is (1.01-1.08):1, and the catalyst accounts for 0.05%-0.35% of the total mass of the reactants (i.e., the total mass of anhydrous methanol and diketene).

[0030] In one embodiment, the catalyst is selected from one or more of propylamine, butylamine, diethylamine, triethylamine, diethylenetriamine, aniline, and diisopropylamine.

[0031] In one embodiment, the reaction temperature ranges from 50 to 120° C.; the residence time ranges from 20 to 60 min; and the reaction pressure ranges from 0.01 to 0.4 MPa.

[0032] In one embodiment, the continuous flow reactor includes a series of continuous production reactors such as microchannel reactors and tubular reactors.

[0033] The crude methyl acetoacetate obtained by the method has a content of 97.9-98.3%, a content of 99.6-99.7% in the finished product after distillation, a product yield of 98.6-98.8%, and an acidity value (HAc) of less than 0.02%.

[0034] In the present invention, the specific operation process is as follows Figure 1 Schematic diagram of the continuous reaction device of diethyl methyl ester and Figure 2 Continuous reaction process of diethyl methyl ester.

[0035] Advantages and effects of the present invention:

[0036] The present invention develops a process method that can effectively dissipate heat and thus control the temperature during the continuous reaction of methyl acetoacetate. First, methanol and a catalyst are respectively pumped in at a certain flow rate ratio. Then, a pump is used to pump out the crude ester in the buffer tank at a certain flow rate, mixed with an alcohol solution, and then the diketene and alcohol ester mixed solution is pumped into a continuous flow reactor at a certain flow rate for reaction. Because the crude ester mixing can timely and effectively dilute the heat generated by the reaction, the temperature in the reactor is stable and controllable, the side reaction is suppressed, the product yield is improved, and the crude ester content obtained is also improved compared with the original continuous process content. Finally, the crude ester obtained after the reaction flows into a condenser for cooling, and then flows into the buffer tank.

[0037] The process of the present invention mainly adds a process of crude ester reflux in a conventional continuous process without reflux, and is a continuous process with crude ester reflux, which does not require a substantial modification of the conventional continuous process. The present invention effectively controls the crude ester reflux ratio (3-15): 1. If the reflux ratio is too low, the crude ester cannot timely neutralize the large amount of heat rapidly released during the esterification process, and if it is too high, it will affect the production capacity.

[0038] This technology is used to circulate crude ester during the continuous reaction process, which effectively solves the problem of heat accumulation in the reactor and the inability to dissipate heat in time, resulting in a rapid temperature rise. It reduces safety hazards, improves product quality and yield, and reduces the temperature resistance requirements for pipeline equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of a continuous reaction device for diethyl methyl ester;

[0040] Figure 2 This is a continuous reaction flow chart of diethyl methyl ester. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] First, methanol and catalyst are pumped into the catalyst mixing section 3 at a certain flow rate from the methanol metering tank 1 and the catalyst metering tank 2 through metering pumps 5 and 6. After the two are mixed, metering pumps 7, 8 and 9 are started, and then diketene, alcohol solution and crude ester in the buffer tank are mixed at u (粗酯) : [u (醇) +u (DK) ]=13:1 is driven into the continuous flow tubular esterification reactor 12, the molar ratio of diketene to methanol is 1.05:1, the diketene feed temperature is controlled to be 5°C, the catalyst is triethylamine, the amount of the catalyst accounts for 0.2% of the total mass of the reactants, the reaction temperature is 90°C, the reaction residence time is 20min, the reaction pressure is adjusted by the pressure regulating valve 13, the reaction pressure is 0.2MPa, the crude ester after the reaction is cooled by the condenser 10 and then flows into the buffer tank 11, the crude ester temperature in the buffer tank is kept at 45°C, the non-condensable gas is emptied, and the crude ester in the buffer tank 11 is driven into the distillation tower by a metering pump for distillation. Due to the inflow of the cooled crude ester in the buffer tank, the heat generated by the reaction is effectively neutralized, there is no heat accumulation, the temperature of each section is stable and controllable (the temperature change of each section can be known through the temperature sensors of each section of the esterification reactor), and the requirements for pipeline equipment are low. The crude ester content obtained after the reaction is 98.3%. After the crude ester is distilled, the content of the product is 99.7%, the product yield is 98.4%, and the acidity (calculated as acetic acid) is 0.017%.

[0044] Embodiment 2:

[0045] Compared with Example 1, the crude ester reflux ratio was adjusted to 4:1, and other processes and parameters remained the same.

[0046] The results show that after the introduction of the crude ester reflux process, the reaction temperature is relatively easy to control, the fluctuation becomes smaller, and it is relatively stable. It is found that the content of dehydroacetic acid and methanol in the crude ester has also decreased. The crude ester reflux amount is smaller than that of Example 1, and the large amount of heat rapidly released during the esterification process cannot be neutralized in time, which still causes the self-polymerization of some diketene and the vaporization of methanol.

[0047] The crude ester content obtained after the reaction is 96.63%. After the crude ester is distilled, the content of the product is 99.4%, the product yield is 93.8%, and the acidity (calculated as acetic acid) is 0.04%.

[0048] Comparative Example 1:

[0049] Compared with Example 1, there is no crude ester reflux (other processes and parameters remain the same), specifically:

[0050] First, methanol and catalyst are pumped into the catalyst mixing section 3 at a certain flow rate ratio from the methanol metering tank 1 and the catalyst metering tank 2 through the metering pumps 5 and 6, respectively. After the two are mixed, the metering pumps 7 and 8 are started to pump the diketene and the alcohol solution into the continuous flow tubular esterification reactor 12, wherein the molar ratio of diketene to methanol is 1.05:1, the diketene feed temperature is controlled to be 5°C, the catalyst is triethylamine, the amount of the catalyst accounts for 0.2% of the total mass of the reactants, the reaction temperature is 90°C, the reaction residence time is 20min, the reaction pressure is adjusted by the pressure regulating valve 13, and the reaction pressure is 0.2MPa. After the reaction, the crude ester is cooled by the condenser 10 and then flows into the buffer tank 11, the crude ester temperature in the buffer tank is maintained at 45°C, the non-condensable gas is emptied, and the crude ester in the buffer tank 11 is pumped into the distillation tower through the metering pump for distillation.

[0051] Due to the intense heat release during the reaction, the temperature of the reaction process is difficult to control stably, and there is local heat accumulation. The temperature is too high, causing diketene to self-polymerize to generate dehydroacetic acid. Methanol is easily vaporized in local locations in the esterification reactor and cannot fully react with diketene. Therefore, the content of methanol and dehydroacetic acid detected in the crude ester is high. Moreover, if the heat accumulates for a long time, it is easy to reduce the life of the reactor and cause the risk of "material impact".

[0052] The crude ester content obtained after the reaction reached 95.84%. After the crude ester was distilled, the content of the product was 99.1%, the product yield was 91.3%, and the acidity (calculated as acetic acid) was 0.14%. Compared with Example 1, the yield and product quality were significantly reduced.

[0053] 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 preparing methyl acetoacetate, characterized in that: The method comprises: injecting methanol and a catalyst into a storage tank to mix to obtain an alcohol solution, then injecting a crude ester in a buffer tank at a certain flow rate, and mixing it with the alcohol solution to obtain an alcohol-ester mixed solution; then injecting diketene DK and the alcohol-ester mixed solution into a continuous flow reactor at a certain flow rate for reaction, and finally the crude ester after the reaction flows through a condenser for cooling, and then flows into the buffer tank at a certain reflux ratio; Among them, the crude ester reflux ratio is: u(crude ester): [u(alcohol) + u(DK)] = 13:1, u is the liquid flow rate, the unit is kg / h; the crude ester temperature in the buffer tank is 45°C; the initial temperature of DK is 5°C; the molar ratio of anhydrous methanol to diketone is 1.05:1; the catalyst accounts for 0.2% of the total mass of anhydrous methanol and diketone; the catalyst is triethylamine; the reaction temperature is 90°C; the residence time is 20min; the reaction pressure is 0.2Mpa; the continuous flow reactor is a continuous flow tubular esterification reactor.

2. The method according to claim 1, characterized in that The reaction formula for preparing methyl acetoacetate is as follows: 。

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