A kind of production method of methyl pyrrolidone

Abstract

The present invention relates to the technical field of methyl pyrrolidone preparation, and discloses a method for producing methyl pyrrolidone. The method comprises the following steps: (1) subjecting a first portion of butyrolactone to a ring-opening reaction with methylamine to obtain a first stream; (2) subjecting the first stream and a second portion of butyrolactone to a ring-forming reaction under a niobium-based catalyst; wherein, in the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 85%. The method uses a niobium-based catalyst as a catalyst in the second stage of cyclodehydration, reduces the adverse effects of water on the reaction, maintains the efficiency of the catalyst, and solves the problems of catalyst instability and low yield of methyl pyrrolidone in the prior art.

Description

Technical Field

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

[0002] N-methylpyrrolidone (NMP) is a polar aprotic solvent with the advantages of high boiling point, strong polarity, low viscosity, strong solubility, no corrosion, low toxicity, good chemical and thermal stability, etc. It is mainly used for aromatic extraction, purification and separation of acetylene, olefins, and dienes, polymer solvents, polymerization reaction solvents, and solvents in the semiconductor preparation process. With the development of new energy vehicles, the demand for NMP is also growing.

[0003] The production technology of N-methylpyrrolidone is mainly synthesized by γ-butyrolactone and methylamine process. The presence of catalyst can accelerate the reaction. Such as molecular sieve catalyst or loaded molecular sieve synthesis process, such as Ce / ZSM-5 (Catal. Commun., 2002, 3, 349-355.) and ZSM-5. But the biggest problem of this type of catalyst is that it is not water-resistant.

[0004] From the reaction point of view, water will be produced during the generation of NMP, which will have a destructive effect on the catalyst, thereby reducing the catalyst activity and shortening the service life of the catalyst. Therefore, a water-resistant acid catalyst will have a continuous catalytic effect on the reaction, and the reaction performance will not gradually decrease due to the presence of water in the system. Therefore, a water-resistant catalyst has better recycling performance, higher economy and application potential. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of poor catalyst stability and low methyl pyrrolidone yield in the preparation process of methyl pyrrolidone, and to provide a production method of methyl pyrrolidone.

[0006] In order to achieve the above object, the present invention provides a method for producing methyl pyrrolidone, which comprises the following steps:

[0007] (1) subjecting the first portion of butyrolactone to a ring-opening reaction with methylamine to obtain a first stream;

[0008] (2) subjecting the first stream and the second portion of butyrolactone to a cyclization reaction under the condition of a niobium-based catalyst;

[0009] Wherein, in the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 85%.

[0010] Preferably, in the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 88%, preferably 90-100%.

[0011] The present invention improves the efficiency of synthesizing methyl pyrrolidone by dividing the reaction into two stages and performing the reaction continuously. The reaction process is divided into two synthesis stages, the first stage is a ring-opening amination stage, and the second stage is a dehydration ring-forming stage. The first stage reaction is controlled to open the butyrolactone ring as much as possible to prepare for the second stage ring-forming reaction; a water-resistant niobium-based catalyst is added to the second stage ring-forming reaction to reduce the adverse effects of water on the catalyst and the reaction during the reaction process, and the water-resistant niobium-based catalyst will maintain the catalytic efficiency and improve the yield of methyl pyrrolidone.

[0012] The inventors found in their research that the presence of water during the reaction process has an adverse effect on the reaction performance. A niobium-based catalyst is used as a catalyst for the second-stage cyclodehydration stage to reduce the adverse effect of water on the reaction, maintain the efficiency of the catalyst, and solve the existing problems of catalyst instability and low yield of methyl pyrrolidone during the reaction. 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 methyl pyrrolidone, which comprises the following steps:

[0015] (1) subjecting the first portion of butyrolactone to a ring-opening reaction with methylamine to obtain a first stream;

[0016] (2) subjecting the first stream and the second portion of butyrolactone to a cyclization reaction under the condition of a niobium-based catalyst;

[0017] Wherein, in the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 85%.

[0018] According to the method of the present invention, preferably, in the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 88%, and more preferably, the yield of hydroxybutyramide is 90-100%.

[0019] By adopting the above technical scheme, the reaction process is divided into two synthesis stages, the first stage is the ring-opening amination stage, and the second stage is the dehydration ring-forming stage. In the first stage, the butyrolactone is opened as much as possible. If the ring-opening reaction in the first stage is insufficient, more severe reaction conditions are required in the second stage to promote the ring-opening of butyrolactone. This process not only causes complex side reactions, which increases the difficulty of subsequent separation, but also increases energy consumption. The present invention controls the degree of ring-opening in the first reaction stage so that the yield of hydroxybutylamide is not less than 85%, and the ring-opening reaction obtains an amide intermediate. In the second reaction stage, a niobium-based catalyst is added to reduce the adverse effects of water on the catalyst, maintain the efficiency of the catalyst, and the two stages are completed independently and continuously, thereby improving the reaction efficiency.

[0020] In the present invention, there is no particular limitation on the amount of the first part of butyrolactone and methylamine in step (1), as long as the ring-opening reaction can be successfully completed. Preferably, the mass ratio of the first part of butyrolactone and methylamine is 1:0.9-4, more preferably 1:1.5-2.5.

[0021] According to the method of the present invention, the conditions of the ring-opening reaction are as long as the yield of the above-mentioned hydroxybutyramide is satisfied. Preferably, the conditions of the ring-opening reaction in step (1) include: a reaction temperature of 190-260°C, a pressure of 0.2-1.5MPa, and a reaction residence time of 5-40min; further preferably, the conditions of the ring-opening reaction in step (1) include: a reaction temperature of 190-240°C, a pressure of 0.2-1.0MPa, and a reaction residence time of 15-30min. The purpose of adopting this preferred embodiment is to allow the ring-opening reaction to react independently, and to be as unaffected as possible by the second step reaction, thereby improving the efficiency of subsequent reactions.

[0022] According to the method of the present invention, the first stream obtained by the ring-opening reaction in step (1) contains hydroxybutyramide and unreacted butyrolactone and methylamine.

[0023] In the present invention, there is no specific limitation on the type of niobium-based catalyst, and those skilled in the art can select it according to actual needs. Preferably, the niobium-based catalyst is selected from at least one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, niobic acid and niobium oxyphosphate. More preferably, the catalyst is at least one of niobium pentoxide, niobic acid and niobium oxyphosphate. The advantage of adopting this preferred embodiment is that the implementation effect of using a niobium-based catalyst with more hydroxyl groups and holes is better.

[0024] The present invention does not particularly limit the preparation method of the niobium-based catalyst, and any preparation method in the prior art can be used in the present invention. Preferably, the following preparation method can be used: dissolving a niobium precursor (preferably niobium pentachloride) in a solvent (preferably water), stirring and hydrolyzing, and then performing solid-liquid separation to obtain a precipitate, washing the precipitate in deionized water until the filtrate is neutral and no Cl ions are detected, and finally drying the washed product to obtain a dry product.

[0025] In a preferred embodiment, the preparation method of the Nb2O5 catalyst is: calcining the above-mentioned dried product to obtain the Nb2O5 catalyst.

[0026] According to the present invention, the specific conditions for stirring can be selected in a wide range. Preferably, the temperature is 20-30°C and the time is 3-10 hours.

[0027] According to the present invention, there is no specific limitation on the method of solid-liquid separation, as long as the purpose of solid-liquid separation is achieved, such as filtration.

[0028] According to the present invention, the drying conditions have a wide range of selections. Preferably, the drying temperature is 80-150° C. and the drying time is 1-10 h.

[0029] According to the present invention, the range of selection of calcination conditions is relatively wide. Preferably, the calcination temperature is 300-700°C and the calcination time is 1-5h.

[0030] In a preferred embodiment, the preparation method of niobium oxyphosphate includes: dispersing niobic acid in a phosphoric acid aqueous solution, stirring and hydrolyzing, then performing solid-liquid separation to obtain a precipitate, washing the precipitate in deionized water until no phosphate ions are detected, and finally drying the washed product. The stirring and drying conditions can be as described above and will not be repeated here.

[0031] In the present invention, there is no specific restriction on the amount of the niobium-based catalyst used in step (2), as long as the cyclization reaction can proceed smoothly. Preferably, the amount of the niobium-based catalyst added is 0.1-10% of the total mass of butyrolactone and methylamine in the first stage, and more preferably, the amount of the niobium-based catalyst added is 0.1-8% of the total mass of butyrolactone and methylamine in the first stage.

[0032] In the present invention, there is no specific restriction on the mixing order of the first stream, the second part of butyrolactone and the niobium-based catalyst in step (2). Preferably, the ring-opening reaction in step (2) comprises: firstly mixing the second part of butyrolactone with the niobium-based catalyst, and contacting the obtained stream with the first stream for reaction.

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

[0034] According to the method of the present invention, there is no specific limitation on the amount of the second part of butyrolactone used in step (2). Preferably, the mass ratio of the second part of butyrolactone to the first part of butyrolactone is 0.5-1:1. This preferred method is more conducive to the cyclization reaction.

[0035] According to the method of the present invention, preferably, the conditions of the cyclization reaction in step (2) include: reaction temperature of 120-200°C, pressure of 0.2-1.5MPa, and reaction residence time of 10-60min; further preferably, the reaction temperature is 140-190°C, pressure of 0.2-1.0MPa, and reaction residence time of 15-45min. The advantage of adopting this preferred embodiment is to improve the reaction efficiency of the second stage, avoid mutual interference between the first stage and the second stage, and enable the niobium-based catalyst to play a better role.

[0036] According to the method of the present invention, preferably, the ring-opening reaction in step (1) and the ring-forming reaction in step (2) are both carried out in a microchannel reactor. The advantage of adopting this preferred embodiment is that the lactone and methylamine are reacted through a microreactor, the materials are fully mixed, the reaction temperature is accurately controlled, the efficiency of reaction mass transfer and heat transfer is improved, the reaction hot spots are eliminated, the role of the catalyst is fully utilized, and the purpose of reducing by-products and improving reaction efficiency is achieved.

[0037] In a preferred embodiment, the inner diameter of the pipe of the microchannel reactor is 0.1-2 mm.

[0038] In a preferred embodiment, the microchannel reactor is made of quartz glass, high borosilicate glass, silicon carbide or polyetheretherketone tube or Hastelloy.

[0039] 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.

[0040] 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.

[0041] 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 into the butyrolactone + methylamine raw material tank, thereby improving the utilization rate of the methylamine.

[0042] 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.

[0043] 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 methyl pyrrolidone is purified to obtain methyl pyrrolidone with higher purity.

[0044] According to the method of the present invention, preferably, the method further comprises separating the catalyst and repeating the above steps (1) to (3) for 15 to 30 times. In the method provided by the present invention, the niobium-based catalyst has excellent stability.

[0045] 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.

[0046] The yield of hydroxybutyramide and the yield of methylpyrrolidone in the present invention are calculated by the following formula:

[0047]

[0048]

[0049] Example 1

[0050] Preparation of Nb2O5 catalyst:

[0051] Weigh 5.0 g (18.5 mmol) of NbCl5 and dissolve it in 150 mL of water. Stir at room temperature for 4 h to obtain a precipitate. Filter the precipitate and wash the filter cake with 500 mL of deionized water until the filtrate is neutral and no Cl ions are detected. Dry the solid product at 120 ° C for 8 h and calcine at 500 ° C for 2 h to obtain a Nb2O5 catalyst.

[0052] The production steps of methyl pyrrolidone are as follows:

[0053] (1) 50 g of the first part of butyrolactone and 75 g of methylamine were placed in a butyrolactone + methylamine raw material tank and mixed thoroughly, the mass ratio of the first part of butyrolactone to the methylamine raw material was 1:1.5, and the mixture was pumped into the first microchannel reactor with a metering pump at an input rate of 5 g / min;

[0054] (2) reacting in the first microchannel reactor at a reaction temperature of 210° C., a pressure of 1.0 MPa, a reaction residence time of 25 min, and detecting a yield of hydroxybutyramide of 93%;

[0055] (3) 25 g of the second part of butyrolactone and 1.3 g of the catalyst were placed in a catalyst + lactone raw material tank and mixed at a flow rate of 1 g / min. The material was pumped into the second microchannel reactor together with the stream obtained in step (2). The reaction temperature was 170° C., the pressure was 0.8 MPa, and the reaction residence time was 30 min.

[0056] (4) After the reaction, the material is transferred to a flash tank for flash evaporation (temperature of 30° C., pressure of 0.05 MPa), and the material obtained after separation of methylamine is sent to a vacuum distillation device (rectification tower) for purification (tower bottom temperature of 60° C., pressure of 0.05 MPa) to obtain methyl pyrrolidone. The material is sampled and analyzed at the outlet of the second microchannel reactor. According to chromatographic analysis, the yield of methyl pyrrolidone is 97.2%.

[0057] (5) The niobium-based catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 97.1%, indicating that the niobium-based catalyst had good stability.

[0058] Example 2

[0059] The method of Example 1 was followed, except that 50.0 g of water of the same mass as that of butyrolactone was added in step (1). Chromatographic analysis showed that the yield of methyl pyrrolidone was 97.1%. The niobium-based catalyst was separated, and then steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 97.0%, indicating that the niobium-based catalyst had good stability.

[0060] Example 3

[0061] Preparation of Nb2O5 nH2O catalyst:

[0062] Weigh 5.0 g (18.5 mmol) of NbCl5 and dissolve it in 150 mL of water. Stir at room temperature for 4 h to obtain a precipitate. Filter the precipitate and wash the filter cake with 500 mL of deionized water until the filtrate is neutral and no Cl ions are detected. Dry the solid product at 120 ° C for 8 h to obtain Nb2O5 nH2O catalyst.

[0063] The production steps of methyl pyrrolidone are as follows:

[0064] (1) 50 g of the first part of butyrolactone and 100 g of methylamine were placed in a butyrolactone + methylamine raw material tank and mixed thoroughly, the mass ratio of the first part of butyrolactone to the methylamine raw material being 1:2, and the mixture was pumped into the first microchannel reactor with a metering pump at an input rate of 3.5 g / min;

[0065] (2) reacting in the first microchannel reactor at a reaction temperature of 200° C., a pressure of 0.6 MPa, a reaction residence time of 23 min, and detecting a yield of hydroxybutyramide of 94%;

[0066] (3) 40 g of the second part of butyrolactone and 3 g of the catalyst were placed in a catalyst + lactone raw material tank and mixed at a flow rate of 0.9 g / min. The material was pumped into the second microchannel reactor together with the stream obtained in step (2). The reaction temperature was 165° C., the pressure was 0.6 MPa, and the reaction residence time was 35 min.

[0067] (4) After the reaction, the material is transferred to a flash tank for flash evaporation (temperature of 20° C., pressure of 0.02 MPa), and the material obtained after separation of methylamine is sent to a vacuum distillation device (rectification tower) for purification (tower bottom temperature of 40° C., pressure of 0.03 MPa) to obtain methyl pyrrolidone. The material is sampled and analyzed at the outlet of the second microchannel reactor. According to chromatographic analysis, the yield of methyl pyrrolidone is 98.5%.

[0068] (5) The niobium-based catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 98.5%, indicating that the niobium-based catalyst had good stability.

[0069] Example 4

[0070] Preparation of Nb2O5 nH2O catalyst:

[0071] Weigh 5.0 g (18.5 mmol) of NbCl5 and dissolve it in 150 mL of water. Stir at room temperature for 4 h to obtain a precipitate. Filter the precipitate and wash the filter cake with 500 mL of deionized water until the filtrate is neutral and no Cl ions are detected. Dry the solid product at 120 ° C for 8 h to obtain Nb2O5 nH2O catalyst.

[0072] The production steps of methyl pyrrolidone are as follows:

[0073] (1) 40 g of the first part of butyrolactone and 72 g of methylamine were placed in a butyrolactone + methylamine raw material tank and mixed thoroughly, the mass ratio of the first part of butyrolactone to the methylamine raw material was 1:1.8, and the mixture was pumped into the first microchannel reactor with a metering pump at an input rate of 4 g / min;

[0074] (2) reacting in the first microchannel reactor at a reaction temperature of 210° C., a pressure of 0.5 MPa, a reaction residence time of 20 min, and detecting a yield of hydroxybutyramide of 92%;

[0075] (3) 32 g of the second part of butyrolactone and 7.8 g of the catalyst were placed in a catalyst + lactone raw material tank and mixed at a flow rate of 1.1 g / min. The material was pumped into the second microchannel reactor together with the stream obtained in step (2). The reaction temperature was 160° C., the pressure was 1 MPa, and the reaction residence time was 40 min.

[0076] (4) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature 45°C, pressure 0.08 MPa), and the material obtained after separating the methylamine was sent to a vacuum distillation device (rectification tower) for purification (tower bottom temperature 20°C, pressure 0.01 MPa) to obtain methyl pyrrolidone. The material was sampled and analyzed at the outlet of the second microchannel reactor. After chromatographic analysis, the yield of methyl pyrrolidone was 98.1%.

[0077] (5) The niobium-based catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 98.1%, indicating that the niobium-based catalyst had good stability.

[0078] Example 5

[0079] Preparation of NbOPO4 catalyst:

[0080] 1.0 g of niobic acid was dispersed in 150 mL of 1 M phosphoric acid aqueous solution and stirred for 24 h. The obtained mixture was filtered and washed with deionized water until no phosphate ions were detected. The obtained solid product was dried at 100 ° C for 12 h to obtain NbOPO4 catalyst.

[0081] The production steps of methyl pyrrolidone are as follows:

[0082] (1) 40 g of the first part of butyrolactone and 96 g of methylamine were placed in a butyrolactone + methylamine raw material tank and mixed thoroughly, the mass ratio of the first part of butyrolactone to the methylamine raw material was 1:2.4, and the mixture was pumped into the first microchannel reactor with a metering pump at an input rate of 4.5 g / min;

[0083] (2) reacting in the first microchannel reactor at a reaction temperature of 240° C., a pressure of 1 MPa, a reaction residence time of 30 min, and detecting a yield of hydroxybutyramide of 97%;

[0084] (3) 40 g of the second part of butyrolactone and 4.1 g of the catalyst were placed in a catalyst + lactone raw material tank and mixed at a flow rate of 1.3 g / min. The material was pumped into the second microchannel reactor together with the stream obtained in step (2). The reaction temperature was 145° C., the pressure was 0.6 MPa, and the reaction residence time was 35 min.

[0085] (4) After the reaction, the material is transferred to a flash tank for flash evaporation (temperature of 30° C., pressure of 0.05 MPa), and the material obtained after separation of methylamine is sent to a vacuum distillation device (rectification tower) for purification (tower bottom temperature of 60° C., pressure of 0.05 MPa) to obtain methyl pyrrolidone. The material is sampled and analyzed at the outlet of the second microchannel reactor. According to chromatographic analysis, the yield of methyl pyrrolidone is 99.3%.

[0086] (5) The niobium-based catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 99.3%, indicating that the niobium-based catalyst had good stability.

[0087] Example 6

[0088] In this embodiment, NbO2 (Aladdin reagent, product number N282626) is used as a catalyst.

[0089] The production steps of methyl pyrrolidone are as follows:

[0090] (1) 40 g of the first part of butyrolactone and 80 g of methylamine were placed in a butyrolactone + methylamine raw material tank and mixed thoroughly, the mass ratio of the first part of butyrolactone to the methylamine raw material was 1:2, and the mixture was pumped into the first microchannel reactor with a metering pump at an input rate of 3.8 g / min;

[0091] (2) reacting in the first microchannel reactor at a reaction temperature of 190° C., a pressure of 0.4 MPa, a reaction residence time of 15 min, and detecting a yield of hydroxybutyramide of 82%;

[0092] (3) 20 g of the second part of butyrolactone and 3 g of the catalyst were placed in a catalyst + lactone raw material tank and mixed at a flow rate of 0.6 g / min. The material was pumped into the second microchannel reactor together with the stream obtained in step (2). The reaction temperature was 190° C., the pressure was 0.8 MPa, and the reaction residence time was 20 min.

[0093] (4) After the reaction, the material was transferred to a flash tank for flash evaporation (temperature of 30° C., pressure of 0.05 MPa), and the material obtained after separation of methylamine was sent to a vacuum distillation device (rectification tower) for purification (tower bottom temperature of 40° C., pressure of 0.01 MPa) to obtain methyl pyrrolidone. The material was sampled and analyzed at the outlet of the second microchannel reactor. According to chromatographic analysis, the yield of methyl pyrrolidone was 84.7%.

[0094] (5) The niobium-based catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 84.3%, indicating that the niobium-based catalyst had good stability.

[0095] Comparative Example 1

[0096] The method of Example 1 was followed, except that HY molecular sieve was used as the catalyst. Chromatographic analysis showed that the yield of methyl pyrrolidone was 68.6%. The catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 37.3%, indicating that the stability of HY molecular sieve catalyst was poor.

[0097] Comparative Example 2

[0098] The method of Example 2 was followed, except that HY molecular sieve was used as the catalyst. Chromatographic analysis showed that the yield of methyl pyrrolidone was 44.9%. The catalyst was separated and steps (1) to (4) were repeated 20 times. The yield of methyl pyrrolidone was 36.5%, indicating that the stability of HY molecular sieve catalyst was poor.

[0099] 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 methyl pyrrolidone, the method comprising the steps of: (1) subjecting the first portion of butyrolactone to a ring-opening reaction with methylamine to obtain a first stream; (2) subjecting the first stream and the second portion of butyrolactone to a cyclization reaction under a niobium-based catalyst; in, In the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 85%.

2. The method according to claim 1, wherein: In the ring-opening reaction of step (1), the yield of hydroxybutyramide is not less than 88%.

3. The method according to claim 2, wherein: In the ring-opening reaction of step (1), the yield of hydroxybutyramide is 90-100%.

4. The method according to claim 1, wherein: In step (1), the mass ratio of the first part of butyrolactone to methylamine is 1:0.9-4.

5. The method according to claim 4, wherein: In step (1), the mass ratio of the first part of butyrolactone to methylamine is 1:1.5-2.

5.

6. The method according to claim 1, wherein: The conditions of the ring-opening reaction in step (1) include: reaction temperature of 190-260° C., pressure of 0.2-1.5 MPa, and reaction residence time of 5-40 min.

7. The method according to claim 6, wherein: The conditions of the ring-opening reaction in step (1) include: reaction temperature of 190-240° C., pressure of 0.2-1.0 MPa, and reaction residence time of 15-30 min.

8. The method according to any one of claims 1 to 7, wherein: The niobium-based catalyst is selected from at least one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, niobic acid and niobium oxyphosphate.

9. The method according to claim 8, wherein: The niobium-based catalyst is selected from at least one of niobium pentoxide, niobic acid and niobium oxyphosphate.

10. The method according to any one of claims 1 to 7, wherein: The amount of the niobium-based catalyst added is 0.1-10% of the total mass of the first part of butyrolactone and methylamine.

11. The method according to claim 10, wherein: The amount of the niobium-based catalyst added is 0.1-8% of the total mass of the first part of butyrolactone and methylamine.

12. The method according to any one of claims 1 to 7, wherein: The mass ratio of the second part of butyrolactone to the first part of butyrolactone is 0.5-1:

1.

13. The method according to any one of claims 1 to 7, wherein: The conditions for the cyclization reaction in step (2) include: reaction temperature of 120-200° C., pressure of 0.2-1.5 MPa, and reaction residence time of 10-60 min.

14. The method according to claim 13, wherein: The conditions for the cyclization reaction in step (2) include: reaction temperature of 140-190° C., pressure of 0.2-1.0 MPa, and reaction residence time of 15-45 min.

15. The method according to any one of claims 1 to 7, wherein: The ring-opening reaction in step (1) and the ring-forming reaction in step (2) are both carried out in a microchannel reactor.

16. The method according to claim 15, wherein: The inner diameter of the pipeline of the microchannel reactor is 0.1-2 mm.

17. The method according to claim 15, wherein: The microchannel reactor is made of quartz glass, high borosilicate glass, silicon carbide or polyetheretherketone tube or Hastelloy.

18. The method according to any one of claims 1 to 7, wherein: The method further comprises flashing the stream obtained from step (2) to separate methylamine.

19. The method according to claim 18, wherein: The flash evaporation conditions include: temperature of 10-50° C. and pressure of 0.02-0.08 MPa.

20. The method according to claim 18, wherein: The method further comprises subjecting the stream obtained by flash distillation to reduced pressure distillation.

21. The method according to claim 20, 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.

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