Method for producing methylpyrrolidone by enzyme catalysis

Abstract

The present invention relates to the technical field of preparation of fine chemical products, and discloses a method for producing methyl pyrrolidone by enzyme catalysis. A method for producing methyl pyrrolidone by enzyme catalysis, the method comprising the following steps: (1) subjecting butyrolactone to a ring-opening reaction in the presence of an enzyme and a solvent to obtain a stream 1; (2) subjecting the stream 1 to a ring-forming reaction with methylamine; wherein, in the ring-opening reaction in step (1), the conversion rate of butyrolactone is not less than 80%. The present invention divides the reaction into two stages, wherein the first stage uses an enzyme catalyst to catalyze the ring-opening reaction, so that the reaction is carried out under reaction conditions close to room temperature, thereby greatly reducing the reaction energy consumption.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of fine chemical products, and in particular to a method for producing methyl pyrrolidone by enzyme catalysis. Background Art

[0002] N-Methylpyrrolidone (NMP) is a polar aprotic solvent in the form of a colorless, transparent oil with high boiling point, low volatility, good thermal stability and strong hygroscopicity. In addition to being used as a traditional solvent for purification, separation and synthesis, it has also been used in the field of new energy vehicles in recent years. As a solvent for dissolving positive electrode binders and as a conductive slurry diffusion liquid, it can improve coating quality and increase the energy density of lithium batteries, and therefore has attracted attention.

[0003] The current mainstream production technology of N-methylpyrrolidone is the synthesis process of γ-butyrolactone and methylamine, which uses relatively high temperature and pressure conditions, which are relatively harsh and have high energy consumption. For example, the synthesis of N-methylpyrrolidone by the non-catalytic reaction of γ-butyrolactone and monomethylamine (CN 1263523A) requires no catalyst to participate in the reaction, and it takes 2-6 hours at a reaction temperature of 250-310°C and a pressure of 3-9MPa. The addition of a catalyst can improve the reaction performance, such as Ce / ZSM-5 catalyst can accelerate the reaction and ease the reaction conditions (Catal. Commun., 2002, 3, 349-355.), but there is still room for further reduction.

[0004] Chemical synthesis is an industry with high energy consumption. At present, under the background of national carbon neutrality and carbon peak, energy conservation and consumption reduction are the baton of chemical product production. Therefore, developing a lower energy consumption and greener N-methylpyrrolidone synthesis process is the future direction of efforts. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of long process and high energy consumption in the production process of N-methylpyrrolidone in the prior art, and to provide a method for producing methylpyrrolidone by enzyme catalysis, which has the advantages of significantly reducing energy consumption and being easy to operate.

[0006] In order to achieve the above object, the present invention provides a method for producing methylpyrrolidone by enzyme catalysis, which comprises the following steps:

[0007] (1) in the presence of an enzyme and a solvent, subjecting butyrolactone to a ring-opening reaction to obtain logistics 1;

[0008] (2) subjecting logistics 1 and methylamine to a ring-forming reaction;

[0009] Wherein, in the ring-opening reaction of step (1), the conversion rate of butyrolactone is not less than 80%;

[0010] Preferably, the enzyme in step (1) is lipase and / or keratinase.

[0011] Preferably, in the ring-opening reaction of step (1), the conversion rate of butyrolactone is 85-100%, preferably 90-100%.

[0012] The present invention divides the reaction into two stages. In the first stage, an enzyme catalyst is used to catalyze the ring-opening reaction, which is carried out under reaction conditions close to room temperature, thereby greatly reducing the reaction energy consumption. The second stage is a ring-forming reaction. The enzyme catalyst used in the first stage of the present invention loses its activity under the reaction conditions of the second stage, so that after the second step of ring-forming, it will not continue to be catalyzed for ring-opening, so the ring-forming rate is greatly improved, thereby improving the reaction efficiency. Moreover, the reaction operation is easy, the equipment requirements are low, and it is easy to achieve scale-up production, and it has good industrialization potential. DETAILED DESCRIPTION

[0013] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0014] The present invention provides a method for producing methylpyrrolidone by enzyme catalysis, which comprises the following steps:

[0015] (1) in the presence of an enzyme and a solvent, subjecting butyrolactone to a ring-opening reaction to obtain logistics 1;

[0016] (2) subjecting logistics 1 and methylamine to a ring-forming reaction;

[0017] Wherein, in the ring-opening reaction of step (1), the conversion rate of butyrolactone is not less than 80%.

[0018] The present invention has a wide range of selection for the type of enzyme in step (1), as long as it can catalyze the ring-opening reaction. Preferably, the enzyme in step (1) is lipase and / or keratinase.

[0019] The present invention has no particular limitation on the source and structure of the lipase and keratinase, and they can be commercially available.

[0020] According to a preferred embodiment of the present invention, the amount of the enzyme used is 1-40% by mass of butyrolactone, preferably 1-15%.

[0021] According to a preferred embodiment of the present invention, relative to 1 g of butyrolactone, the dosage of the enzyme is 1000-80000 U, preferably 1000-30000 U. In the present invention, the "U" is the enzyme activity unit.

[0022] The present invention has a wide range of choices for the type and amount of the solvent in step (1), as long as it can provide a reaction environment for the ring-opening reaction in step (1). Preferably, the solvent is selected from at least one of low-carbon alcohols, low-carbon hydrocarbons and water, and is more preferably low-carbon alcohols.

[0023] Preferably, the low-carbon alcohol is selected from at least one of methanol, ethanol, propanol and butanol, more preferably methanol and / or ethanol. This preferred embodiment is more conducive to better dispersion of the substrate and more conducive to the ring-opening reaction of butyrolactone.

[0024] The low-carbon hydrocarbon may be a C1-C8 hydrocarbon. Preferably, the low-carbon hydrocarbon is selected from at least one of cyclohexane, n-hexane and cyclopentane.

[0025] According to a preferred embodiment of the present invention, in step (1), the molar ratio of butyrolactone to solvent is 1:0.1-2, preferably 1:0.1-0.6.

[0026] According to a preferred embodiment of the present invention, methylamine is also added in the ring-opening reaction process of step (1), and the amount of methylamine added is 0.1-1% based on the total mass of butyrolactone and the solvent. This preferred embodiment is more conducive to fully activating the enzyme activity.

[0027] In the present invention, the methylamine can be provided in the form of a solution, such as an aqueous solution. The concentration of the methylamine aqueous solution can be 10-50% by weight. In the present embodiment, 30% by weight is used as an example for illustration.

[0028] Preferably, the conditions of the ring-opening reaction in step (1) include: reaction temperature of 20-60°C, pressure of 0.1-0.5MPa, and reaction time of 5-24h; preferably, reaction temperature of 30-55°C, pressure of 0.1-0.2MPa, and reaction time of 6-16h. By adopting the method provided by the present invention, step (1) can be reacted under relatively mild conditions, greatly reducing energy consumption, and is suitable for scale-up production.

[0029] According to the method of the present invention, preferably, in the ring-opening reaction of step (1), the conversion rate of butyrolactone is 85-100%, preferably 90-100%. This preferred embodiment is more conducive to the second step of ring-forming reaction.

[0030] According to the present invention, preferably, no catalyst is added in step (2). In the method provided by the present invention, an enzyme catalyst is used to catalyze the ring-opening reaction in the first stage, and the enzyme catalyst loses its activity under the reaction conditions of the second stage. Preferably, no additional catalyst is added, so that after the ring is formed in the second step, the ring-opening will not be further catalyzed.

[0031] In the present invention, there is no particular limitation on the amount of methylamine used in step (2). Preferably, the molar ratio of butyrolactone in step (1) to methylamine in step (2) is 1:1-4, preferably 1:1-1.5.

[0032] According to the present invention, preferably, the conditions for the cyclization reaction in step (2) include: reaction temperature of 180-300°C, pressure of 1.0-4.0MPa, and reaction time of 60-180min; further preferably, the reaction temperature is 200-260°C, pressure of 1.0-3.0MPa, and reaction time of 60-150min.

[0033] In the present invention, the logistics obtained by the cyclization reaction in step (2) includes N-methylpyrrolidone and unreacted material components.

[0034] According to the method of the present invention, preferably, the ring-opening reaction described in step (1) and the ring-forming reaction described in step (2) are both carried out in the same reactor. The advantage of adopting this preferred embodiment is that the entire reaction can be carried out in one reactor, and the size of the reactor can be customized according to actual needs, so as to easily realize the amplified production of the reaction and shorten the experimental process from small test to production. In addition, the ring-opening reaction stage and the ring-forming reaction stage can be independently controlled and carried out, and the operation window is wide.

[0035] According to the method of the present invention, preferably, the method further comprises step (3): separating methylamine from the stream obtained in step (2). The purpose of adopting this preferred embodiment is to remove methylamine from the target product, reduce its adverse effect on the subsequent target product purification process, and improve the yield of the target product.

[0036] In a preferred embodiment, the separation in step (3) is carried out in a flash tank. The reaction conditions in the flash tank can be selected in a wide range as long as methylamine can be separated. In a preferred embodiment, the temperature in the flash tank is 10-50° C. and the pressure is 0.02-0.08 MPa.

[0037] The method according to the present invention further comprises a buffering stage. Preferably, the method further comprises recycling the methylamine separated in step (3) back to the buffer tank, so that the methylamine is temporarily stored in the buffer tank and then recycled as a raw material for the next kettle, thereby improving the utilization rate of the methylamine.

[0038] According to the method of the present invention, preferably, the method comprises subjecting the material obtained in step (3) (the material obtained after separating methylamine) to reduced pressure distillation.

[0039] In a preferred case, the conditions of the reduced pressure distillation include: a bottom temperature of 10-60° C. and a pressure of 0.01-0.05 MPa. The advantage of adopting this preferred embodiment is that the target product N-methylpyrrolidone is purified to obtain N-methylpyrrolidone with higher purity.

[0040] The present invention will be described in detail below by way of examples. In the following examples, all raw materials used are commercially available unless otherwise specified.

[0041] The conversion rate of butyrolactone and the yield of N-methylpyrrolidone in the present invention are calculated by the following formula:

[0042]

[0043]

[0044] The enzyme information used in the examples is as follows: keratinase, 25 kg bag, Hubei Xinrunde Chemical Co., Ltd., enzyme activity 200,000 U / g. Lipase, enzyme activity 100,000 U / g, 25 kg bag, Hubei Jushuo Biotechnology Co., Ltd.

[0045] Example 1

[0046] The production steps of N-methylpyrrolidone are as follows:

[0047] (1) 5 g of butyrolactone and 0.6 g of methanol are placed in a reaction kettle, the molar ratio of butyrolactone / methanol is 1 / 0.3, and the total amount of butyrolactone and methanol is 5.6 g. A 30 wt % methylamine aqueous solution is then added, and the amount of methylamine added accounts for 0.5% of the total mass of butyrolactone and methanol, based on the mass of methylamine.

[0048] (2) Add keratinase to the reaction kettle and stir evenly. The mass of the added keratinase accounts for 15% of the mass of the added butyrolactone.

[0049] (3) The mixed solution was heated to 45° C. under air atmosphere, the reaction pressure was maintained at 0.1 MPa, the reaction time was 12 h, and after reaction, the butyrolactone conversion rate was detected to be 98.2%.

[0050] (4) Continue to add methylamine to the reaction kettle, and the molar ratio of butyrolactone to methylamine is 1:1.2 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 230° C., a reaction pressure of 2 MPa, and a reaction time of 90 minutes.

[0051] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature: 25°C, pressure: 0.04MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device for purification (bottom temperature: 50°C, pressure: 0.01MPa) to obtain N-methylpyrrolidone. The sample was taken and analyzed by chromatography, and the yield of N-methylpyrrolidone was 99.2%.

[0052] Example 2

[0053] The production steps of N-methylpyrrolidone are as follows:

[0054] (1) 5 g of butyrolactone and 1.1 g of ethanol are placed in a reaction kettle, the molar ratio of butyrolactone / ethanol is 1 / 0.4, and the total amount of butyrolactone and ethanol is 6.1 g. A 30 wt % methylamine aqueous solution is then added, and the amount of methylamine added accounts for 0.3% of the total mass of butyrolactone and ethanol, based on the mass of methylamine.

[0055] (2) Add keratinase to the reaction kettle and stir evenly. The mass of the added keratinase accounts for 6% of the mass of the added butyrolactone.

[0056] (3) The mixed solution was heated to 35° C. under air atmosphere, the reaction pressure was maintained at 0.2 MPa, the reaction time was 16 h, and after reaction, the butyrolactone conversion rate was detected to be 95.8%.

[0057] (4) Continue to add methylamine to the reactor, and the molar ratio of butyrolactone to methylamine is 1:1.5 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 240° C., a reaction pressure of 2 MPa, and a reaction time of 100 minutes.

[0058] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature: 30°C, pressure: 0.02MPa), and the material obtained after separation of methylamine was placed in a vacuum distillation apparatus for purification (bottom temperature: 30°C, pressure: 0.03MPa) to obtain N-methylpyrrolidone. The sample was taken for chromatographic analysis, and the yield of N-methylpyrrolidone was 96.5%.

[0059] Example 3

[0060] The production steps of N-methylpyrrolidone are as follows:

[0061] (1) 5 g of butyrolactone and 1.3 g of ethanol are placed in a reaction kettle, the molar ratio of butyrolactone / ethanol is 1 / 0.5, and the total amount of butyrolactone and ethanol is 6.3 g. A 30 wt % methylamine aqueous solution is then added, and the amount of methylamine added accounts for 0.6% of the total mass of butyrolactone and ethanol, based on the mass of methylamine.

[0062] (2) Add lipase to the reaction kettle and stir evenly. The mass of the added lipase accounts for 10% of the mass of the added butyrolactone.

[0063] (3) The mixed solution was heated to 40° C. under air atmosphere, the reaction pressure was maintained at 0.1 MPa, the reaction time was 12 h, and after reaction, the butyrolactone conversion rate was detected to be 92.4%.

[0064] (4) Continue to add methylamine to the reaction kettle, and the molar ratio of butyrolactone to methylamine is 1:1.5 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 220° C., a reaction pressure of 1.5 MPa, and a reaction time of 120 minutes.

[0065] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature 40°C, pressure 0.06MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device for purification (bottom temperature 60°C, pressure 0.05MPa) to obtain N-methylpyrrolidone. Samples were taken and analyzed by chromatography, and the yield of N-methylpyrrolidone was 93.6%.

[0066] Example 4

[0067] The production steps of N-methylpyrrolidone are as follows:

[0068] (1) 5 g of butyrolactone and 0.6 g of methanol are placed in a reaction kettle, the molar ratio of butyrolactone / methanol is 1 / 0.3, and the total amount of butyrolactone and methanol is 5.6 g. A 30 wt % methylamine aqueous solution is then added, and the amount of methylamine added accounts for 0.2% of the total mass of butyrolactone and methanol, based on the mass of methylamine.

[0069] (2) Add lipase of mass 200 g to the reactor and stir evenly. The mass of the added lipase accounts for 8% of the mass of the added butyrolactone.

[0070] (3) The mixed solution was heated to 40° C. under air atmosphere, the reaction pressure was maintained at 0.1 MPa, the reaction time was 8 h, and after reaction, the butyrolactone conversion rate was detected to be 91.8%.

[0071] (4) Continue to add methylamine to the reaction kettle, and the molar ratio of butyrolactone to methylamine is 1:2 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 240° C., a reaction pressure of 2.5 MPa, and a reaction time of 90 minutes.

[0072] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature: 35°C, pressure: 0.04MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device for purification (bottom temperature: 25°C, pressure: 0.02MPa) to obtain N-methylpyrrolidone. The sample was taken and analyzed by chromatography, and the yield of N-methylpyrrolidone was 92.4%.

[0073] Example 5

[0074] The production steps of N-methylpyrrolidone are as follows:

[0075] (1) 5 g of butyrolactone and 0.8 g of ethanol are placed in a reaction kettle, the molar ratio of butyrolactone / ethanol is 1 / 0.3, and the total amount of butyrolactone and ethanol is 5.8 g. A 30 wt % methylamine aqueous solution is then added, and the amount of methylamine added accounts for 0.8% of the total mass of butyrolactone and ethanol, based on the mass of methylamine.

[0076] (2) adding keratinase to the reaction kettle and stirring evenly, wherein the mass of the added keratinase accounts for 3% of the mass of the added butyrolactone;

[0077] (3) The mixed solution was heated to 50° C. under air atmosphere, the reaction pressure was maintained at 0.1 MPa, the reaction time was 7 h, and after reaction, the butyrolactone conversion rate was detected to be 91.5%.

[0078] (4) Continue to add methylamine to the reaction kettle, and the molar ratio of butyrolactone to methylamine is 1:1.2 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 250° C., a reaction pressure of 2 MPa, and a reaction time of 70 minutes.

[0079] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature: 35°C, pressure: 0.05MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device for purification (bottom temperature: 40°C, pressure: 0.01MPa) to obtain N-methylpyrrolidone. The sample was taken for chromatographic analysis, and the yield of N-methylpyrrolidone was 93.1%.

[0080] Example 6

[0081] The production steps of N-methylpyrrolidone are as follows:

[0082] (1) 5 g of gbutyrolactone and 0.8 g of ethanol were placed in a reaction kettle, the molar ratio of gbutyrolactone / ethanol was 1 / 0.3, and the total amount of gbutyrolactone and ethanol was 5.8 g.

[0083] (2) Add keratinase to the reaction kettle and stir evenly. The mass of the added keratinase accounts for 3% of the mass of the added butyrolactone.

[0084] (3) The mixed solution was heated to 50° C. under air atmosphere, the reaction pressure was maintained at 0.1 MPa, the reaction time was 7 h, and after reaction, the butyrolactone conversion rate was detected to be 80.7%.

[0085] (4) Continue to add methylamine to the reaction kettle, and the molar ratio of butyrolactone to methylamine is 1:1.2 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 250° C., a reaction pressure of 2 MPa, and a reaction time of 70 minutes.

[0086] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature of 35°C, pressure of 0.05 MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device for purification (bottom temperature of 40°C, pressure of 0.01 MPa) to obtain N-methylpyrrolidone. The sample was taken and analyzed by chromatography, and the yield of N-methylpyrrolidone was 87.1%.

[0087] Comparative Example 1

[0088] Comparative Example 1 is the same as Example 1, except that no enzyme catalyst is added. Samples were taken and analyzed by chromatography, and the yield of N-methylpyrrolidone was 33.8%.

[0089] Comparative Example 2

[0090] In Comparative Example 2, no enzyme catalyst was added, but the relevant reaction conditions of step (3) were improved.

[0091] The production steps of N-methylpyrrolidone are as follows:

[0092] (1) 5 g of butyrolactone and 0.6 g of methanol are placed in a reaction kettle, the molar ratio of butyrolactone / methanol is 1 / 0.3, and the total amount of butyrolactone and methanol is 5.6 g. A 30 wt % methylamine aqueous solution is then added, and the amount of methylamine added accounts for 0.5% of the total mass of butyrolactone and methanol, based on the mass of methylamine.

[0093] (2) Stir well.

[0094] (3) The mixed solution was heated to 170° C. under air atmosphere, the reaction pressure was maintained at 1 MPa, the reaction time was 12 h, and after reaction, the butyrolactone conversion rate was detected to be 18.2%.

[0095] (4) Continue to add methylamine to the reaction kettle, and the molar ratio of butyrolactone to methylamine is 1:1.2 based on the molar amount of butyrolactone added in step (1). Heat the reaction system to a reaction temperature of 230° C., a reaction pressure of 2 MPa, and a reaction time of 90 minutes.

[0096] (5) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature: 25°C, pressure: 0.04MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device for purification (bottom temperature: 50°C, pressure: 0.01MPa) to obtain N-methylpyrrolidone. The sample was taken for chromatographic analysis, and the yield of N-methylpyrrolidone was 39.4%.

[0097] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for producing methylpyrrolidone by enzyme catalysis, the method comprising the following steps: (1) in the presence of an enzyme and a solvent, subjecting butyrolactone to a ring-opening reaction to obtain logistics 1; (2) subjecting logistics 1 and methylamine to a cyclization reaction; in, In the ring-opening reaction of step (1), the conversion rate of butyrolactone is not less than 80%; Wherein, the enzyme in step (1) is keratinase.

2. The method according to claim 1, wherein: The dosage of the enzyme is 1-40% of the mass of butyrolactone.

3. The method according to claim 2, wherein: The dosage of the enzyme is 1-15% of the mass of butyrolactone.

4. The method according to claim 1, wherein: Relative to 1 g of butyrolactone, the dosage of the enzyme is 1000-80000 U.

5. The method according to claim 4, wherein: Relative to 1 g of glucopyranoside, the dosage of the enzyme is 1000-30000 U.

6. The method according to claim 1, wherein: The solvent is selected from at least one of low-carbon alcohols, low-carbon hydrocarbons and water; The low-carbon alcohol is selected from at least one of methanol, ethanol, propanol and butanol; The low carbon hydrocarbon is selected from at least one of cyclohexane, n-hexane and cyclopentane.

7. The method according to claim 6, wherein: The solvent is a low carbon alcohol.

8. The method according to claim 1, wherein: In step (1), the molar ratio of butyrolactone to the solvent is 1:0.1-2.

9. The method according to claim 8, wherein: In step (1), the molar ratio of butyrolactone to the solvent is 1:0.1-0.

6.

10. The method according to claim 1, wherein: In the ring-opening reaction process of step (1), methylamine is also added, and the amount of methylamine added is 0.1-1% based on the total mass of butyrolactone and the solvent.

11. The method according to any one of claims 1 to 10, wherein: The conditions of the ring-opening reaction in step (1) include: reaction temperature of 20-60° C., pressure of 0.1-0.5 MPa, and reaction time of 5-24 h.

12. The method according to claim 11, wherein: The conditions of the ring-opening reaction in step (1) include: reaction temperature of 30-55° C., pressure of 0.1-0.2 MPa, and reaction time of 6-16 h.

13. The method according to any one of claims 1 to 10, wherein: In the ring-opening reaction of step (1), the conversion rate of butyrolactone is 85-100%.

14. The method according to claim 13, wherein: In the ring-opening reaction of step (1), the conversion rate of butyrolactone is 90-100%.

15. The method according to any one of claims 1 to 10, wherein: The molar ratio of butyrolactone in step (1) to methylamine in step (2) is 1:1-4.

16. The method according to claim 15, wherein: The molar ratio of butyrolactone in step (1) to methylamine in step (2) is 1:1-1.

5.

17. The method according to any one of claims 1 to 10, wherein: The conditions for the cyclization reaction in step (2) include: reaction temperature of 180-300° C., pressure of 1.0-4.0 MPa, and reaction time of 60-180 min.

18. The method according to claim 17, wherein: The conditions for the cyclization reaction in step (2) include: reaction temperature of 200-260° C., pressure of 1.0-3.0 MPa, and reaction time of 60-150 min.

19. The method according to any one of claims 1 to 10, wherein: The method further comprises step (3): separating methylamine from the logistics obtained in step (2).

20. The method according to claim 19, wherein: The separation in step (3) is carried out in a flash tank.

21. The method according to claim 20, wherein: The temperature in the flash tank is 10-50° C., and the pressure is 0.02-0.08 MPa.

22. The method according to claim 19, wherein: The method comprises subjecting the logistics obtained in step (3) to reduced pressure distillation.

23. The method according to claim 22, wherein: The conditions of the reduced pressure distillation include: a bottom temperature of 10-60° C. and a pressure of 0.01-0.05 MPa.

24. The method according to any one of claims 1 to 10, wherein: The ring-opening reaction in step (1) and the ring-forming reaction in step (2) are carried out in the same reactor.

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