A process for the production of n-methylpyrrolidone

Abstract

The application provides a short-process and low-carbon-emission N-methyl pyrrolidone industrial chain production process, which focuses on synthesizing N-methyl pyrrolidone by reacting monomethylamine and gamma-butyrolactone raw materials, thereby saving a methylamine separation tower and solving the problem of difficult external sale of dimethylamine; compared with similar devices, the production process flow is effectively shortened, the N-methyl pyrrolidone industrial chain production cost is greatly reduced, meanwhile, by-products brought by the production process are effectively recycled by taking advantage of the chemical industrial park, and the carbon emission is greatly reduced; the N-methyl pyrrolidone product prepared by the application is extremely competitive.

Description

Technical Field

[0001] This invention relates to the field of N-methylpyrrolidone technology, specifically to a short-process, low-carbon emission N-methylpyrrolidone industrial chain production process. Background Technology

[0002] N-Methylpyrrolidone (NMP) is a nitrogen-containing heterocyclic compound with a series of excellent physical and chemical properties. It is a highly efficient and selective solvent that is non-toxic, has a high boiling point, strong polarity, low viscosity, low corrosiveness, high solubility, low volatility, good stability, and is easily recyclable. It is widely used in petrochemicals, high-precision electronics, circuit boards, and lithium batteries. NMP is a crucial auxiliary material in the production of lithium-ion battery electrodes, primarily used to dissolve / swell PVDF and dilute slurries. The quality of NMP products directly impacts the production and quality of high-end electronic products.

[0003] Currently, NMP is synthesized by reacting γ-butyrolactone (GBL) with methylamine. In mainstream NMP production processes, the methylamine feedstock is typically an aqueous solution of monomethylamine or monomethylamine itself. However, the production process using an aqueous solution of monomethylamine generates a large amount of wastewater that requires treatment. The reaction temperature and pressure using monomethylamine are also relatively high. Most importantly, monomethylamine is synthesized from methanol and liquid ammonia, and its production also generates a significant amount of dimethylamine as a byproduct. Without downstream supporting facilities, the dimethylamine must be sold externally, and the domestic dimethylamine market is currently sluggish. BASF's published patent uses mixed methylamines to synthesize NMP, but the reaction rates of monomethylamine, dimethylamine, and trimethylamine with GBL decrease in that order, with trimethylamine having the slowest reaction rate, posing a risk of trimethylamine accumulation. Furthermore, the required reaction pressure and residence time are longer, resulting in higher equipment investment.

[0004] To address this, existing technologies have disclosed improvements to the synthesis of NMP from mixed methylamines. For example, CN116283704A discloses a continuous method for preparing N-methylpyrrolidone, comprising: mixing raw materials in a first mixer, then passing them through a heat exchanger into a reaction column I packed with a balanced catalyst; the generated monomethylamine, dimethylamine, and trimethylamine continuously flow from the bottom of the column into a distillation column I, removing unreacted ammonia from the system; the ammonia is removed as a first light component at the top of the distillation column I, and the bottom distillate is the first heavy component, which flows into a reaction column II, where dimethylamine and trimethylamine undergo hydrolysis to generate monomethylamine; then the mixture flows into a second mixer, where it is mixed with γ-butyrolactone in the second mixer and flows into a reaction column III for the N-methylpyrrolidone synthesis reaction; after the reaction is complete, the mixture is distilled into a distillation column II, and the second heavy component, crude N-methylpyrrolidone, is obtained from the bottom of the column and further purified in a distillation column III, with the third light component at the top being N-methylpyrrolidone. Compared to directly using a monomethylamine solution, this method reduces raw material and processing costs; and compared to directly reacting mixed methylamines with γ-butyrolactone, it can better improve the conversion rate of GBL. However, this technical solution uses a mixed aqueous solution mainly containing monomethylamine as raw material (dimethylamine content 0-2wt%, trimethylamine content 0-4wt%, water content 30-50%), which then reacts with γ-butyrolactone to prepare N-methylpyrrolidone. The utilization rate of mixed methylamine, especially monomethylamine, as raw material is low, resulting in high production costs.

[0005] Therefore, there is a need to develop a new production process for the N-methylpyrrolidone industrial chain to shorten the process, save production costs, and reduce carbon emissions. Summary of the Invention

[0006] To address the technical challenges of high production costs, difficulty in selling byproducts, and high carbon emissions in the NMP production process, this invention provides a short-process, low-carbon-emission N-methylpyrrolidone industrial chain production process. This process primarily utilizes a mixture of dimethylamine and γ-butyrolactone as raw materials to synthesize N-methylpyrrolidone. This not only eliminates the need for a methylamine separation tower but also solves the problem of difficult-to-sell dimethylamine, effectively shortening the production process, reducing carbon emissions, and lowering production costs.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a short-process, low-carbon emission N-methylpyrrolidone industrial chain production process, the industrial chain production process comprising:

[0009] Methanol and liquid ammonia are mixed and heated to carry out a methylamine synthesis reaction. The methylamine reaction product is then subjected to deammoniation, water extraction, and dehydration to obtain mixed methylamine, methanol waste liquid, and recycled water.

[0010] The mixture of the methylamine and γ-butyrolactone raw materials was cooled and then subjected to N-methylpyrrolidone synthesis reaction after being pressurized and heated. The N-methylpyrrolidone reaction product was subjected to demethylamine to obtain liquid-phase mixed amine and crude N-methylpyrrolidone. The crude N-methylpyrrolidone was then purified to obtain liquid-phase heavy components and N-methylpyrrolidone products.

[0011] The production process described in this invention focuses on the reaction of dimethylamine and γ-butyrolactone as raw materials to synthesize N-methylpyrrolidone. This not only saves on the methylamine separation tower but also solves the problem of the difficulty in selling dimethylamine externally, effectively shortening the production process, reducing carbon emissions, and lowering production costs.

[0012] As a preferred technical solution of the present invention, the γ-butyrolactone raw material is obtained by the following preparation method:

[0013] 1,4-Butanediol is mixed with recycled hydrogen and preheated to carry out the γ-butyrolactone synthesis reaction. The resulting γ-butyrolactone reaction product is cooled to obtain a gaseous product and a crude liquid product. A portion of the gaseous product is returned as recycled hydrogen, and the other portion is recycled. The crude liquid product is purified to remove light components and obtain light component impurities and the γ-butyrolactone raw material. The light component impurities include tetrahydrofuran and butanol, and the γ-butyrolactone raw material contains γ-butyrolactone and heavy component impurities.

[0014] In existing technologies, the production of GBL using the BDO method requires the removal of light and heavy components to obtain the GBL product, resulting in high equipment investment and operating costs. However, the production process described in this invention utilizes the fact that the boiling points of GBL and NMP are close, employing γ-butyrolactone raw materials containing both γ-butyrolactone and heavy component impurities for the synthesis of N-methylpyrrolidone. The heavy component impurities can enter the liquid phase during N-methylpyrrolidone purification, thus achieving removal without affecting the purity of the N-methylpyrrolidone product. Therefore, the production process described in this invention eliminates the need for a GBL removal tower, effectively saving investment and reducing operating costs.

[0015] As a preferred technical solution of the present invention, 1,4-butanediol (BDO) is atomized under high pressure and then mixed with preheated circulating hydrogen. The hydrogen-to-ethanol ratio is controlled at 12-16, such as 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5 or 16, and the pressure is controlled at 0.3-0.5 MPaG, such as 0.3 MPaG, 0.35 MPaG, 0.4 MPaG, 0.45 MPaG or 0.5 MPaG.

[0016] Preferably, the cold point temperature of the γ-butyrolactone synthesis reaction is controlled at 180~210℃, such as 180℃, 185℃, 190℃, 195℃, 200℃, 205℃ or 210℃.

[0017] The γ-butyrolactone synthesis reaction described in this invention is carried out in a tubular reactor, with Wanhua's self-developed catalyst inside the tubes, as detailed in CN117599809A.

[0018] Preferably, the light-weight refining process is carried out using a GBL light-weight refining tower, with the tower top pressure controlled at 10~15 kPaA, for example 10 kPaA, 11 kPaA, 12 kPaA, 13 kPaA, 14 kPaA, or 15 kPaA, etc., the tower top temperature controlled at 75~90℃, for example 75℃, 80℃, 85℃, or 90℃, etc., and the reflux ratio controlled at 5.0~15.0, for example 5.0, 7.0, 8.0, 10.0, 1... The temperature of the column bottom is controlled at 130~140℃, such as 130℃, 131℃, 133℃, 135℃, 137℃, 138℃ or 140℃, etc.; the liquid phase collected from the column bottom is γ-butyrolactone raw material containing γ-butyrolactone and heavy component impurities; the distillate from the top of the column is the light component impurities, which is sent to the park for further recovery of tetrahydrofuran and butanol; the non-condensable gas from the top of the column is absorbed by the circulating liquid of the vacuum unit and then sent for incineration.

[0019] As a preferred embodiment of the present invention, the methylamine reaction product is deaminated to obtain an azeotrope and a deaminated heavy component; the deaminated heavy component is extracted with water as an extractant to obtain a mixed amine light component and a mixed amine aqueous solution; the mixed amine aqueous solution is dehydrated to obtain the mixed methylamine, methanol waste liquid and recycled water;

[0020] The azeotrope and the light component of the mixed amine are returned to the methylamine synthesis reaction and used as raw materials to mix with methanol and liquid ammonia; part of the recycled water is returned to the water extraction process as an extractant, and the other part enters the park's biochemical system.

[0021] The industrial chain production process described in this invention can not only recycle the separated impurity-containing streams, but also recycle the by-products involved by leveraging the advantages of the large platform of the industrial park, thereby realizing the advantages of industrial chain integration and significantly reducing production costs and carbon emissions.

[0022] As a preferred technical solution of the present invention, the methanol waste liquid enters the methanol recovery tower for treatment, the recovered methanol obtained from the top of the tower is returned to the methylamine synthesis reaction as raw material methanol, and the wastewater obtained from the bottom of the tower enters the park's biochemical system.

[0023] Preferably, the pressure of the methanol recovery tower is controlled at 50~100 kPaG, such as 50 kPaG, 60 kPaG, 70 kPaG, 80 kPaG, 90 kPaG, or 100 kPaG; the top temperature is controlled at 60~80℃, such as 60℃, 65℃, 70℃, 75℃, or 80℃; the reflux ratio is controlled at 10.0~20.0, such as 10.0, 11.0, 13.0, 15.0, 17.0, 19.0, or 20.0; and the bottom temperature is controlled at 110~115℃, such as 110℃, 111℃, 112℃, 113℃, 114℃, or 115℃. The distillate from the top of the methanol recovery tower is returned to the methylamine synthesis reaction as raw material methanol, while the non-condensable gas is sent to the tail gas absorption system to recover mixed amines and methanol.

[0024] As a preferred technical solution of the present invention, methanol and liquid ammonia are mixed and pressurized to 2.6~3.2 MPaG, such as 2.6 MPaG, 2.7 MPaG, 2.8 MPaG, 2.9 MPaG, 3.0 MPaG, 3.1 MPaG or 3.2 MPaG, and then heated to 320~360℃, such as 320℃, 330℃, 340℃, 350℃ or 360℃.

[0025] Preferably, the feed N / C ratio for the methylamine synthesis reaction is 1.2 to 2.2:1, such as 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2.0:1, or 2.2:1.

[0026] In this invention, the N / C ratio of the feed for the methylamine synthesis reaction refers to the molar ratio of nitrogen to carbon in the feed. When the light component of the mixed amine obtained by water extraction and the small portion of the mono- and di-mixed methylamine obtained by dehydration are returned to the methylamine synthesis reaction as a mixed amine, and when the azeotrope obtained by deammoniation is returned to the methylamine synthesis reaction, the total feed N / C obtained after mixing the four materials—methanol, liquid ammonia, mixed amine, and azeotrope—refers to the molar ratio of nitrogen to carbon in the total feed.

[0027] Preferably, the reaction temperature of the methylamine synthesis reaction is controlled at 390~420℃, for example 390℃, 395℃, 400℃, 405℃, 410℃, 415℃ or 420℃.

[0028] As a preferred embodiment of the present invention, the ammonia removal is carried out using an ammonia removal tower, with the tower top pressure controlled at 1.7~1.9 MPaG, such as 1.7MPaG, 1.75MPaG, 1.8MPaG, 1.85MPaG, or 1.9MPaG, etc., and the tower top temperature controlled at 45~50℃, such as 45℃, 46℃, 47℃, 48℃, 49℃, or 50℃, etc., and the reflux ratio controlled at 1.0~2. 0, for example 1.0, 1.1, 1.3, 1.5, 1.7, 1.8 or 2.0, etc., the bottom temperature of the column is controlled at 115~125℃, for example 115℃, 117℃, 118℃, 120℃, 121℃, 123℃ or 125℃, etc., the liquid phase collected from the bottom of the column is used for the water extraction; the non-condensable gas at the top of the column is sent to the tail gas absorption system to recover ammonia and mixed amines, and the distillate at the top of the column is returned to the methylamine synthesis reaction as an azeotrope.

[0029] As a preferred embodiment of the present invention, the water extraction is carried out using an extraction tower. The pressure of the extraction tower is controlled at 0.8~0.9 MPaG, for example, 0.8MPaG, 0.81MPaG, 0.83MPaG, 0.85MPaG, 0.86MPaG, 0.88MPaG, or 0.9MPaG, etc. The volume ratio of water as the extractant to the feed is controlled at 0.8~2:1, for example, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.3:1, 1.5:1, 1.6:1, 1.8:1, or 2:1, etc. The top temperature is controlled at 78~84℃, such as 78℃, 79℃, 80℃, 81℃, 82℃, 83℃ or 84℃, etc.; the reflux ratio is controlled at 1.0~2.0, such as 1.0, 1.1, 1.3, 1.5, 1.7, 1.9 or 2.0, etc.; the bottom temperature is controlled at 148~156℃, such as 148℃, 150℃, 152℃, 154℃ or 156℃, etc.; the liquid phase collected from the bottom is used for the aforementioned dehydration; the distillate from the top of the column is the light component of the mixed amine, which is returned to the methylamine synthesis reaction to participate in the reaction; the non-condensable gas from the top of the column is sent to the tail gas absorption system to recover the mixed amine.

[0030] As a preferred embodiment of the present invention, the dehydration is carried out using a dehydration tower. The pressure of the dehydration tower is controlled at 0.5~0.6 MPaG, for example, 0.5MPaG, 0.53MPaG, 0.55MPaG, 0.58MPaG, or 0.6MPaG, etc. The tower top temperature is controlled at 50~56℃, for example, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, or 56℃, etc., and the reflux ratio is controlled at 2.0~4.0. For example, 2.0, 2.5, 3.0, 3.5 or 4.0, etc., the bottom temperature of the column is controlled at 162~165℃, such as 162℃, 163℃, 164℃ or 165℃, etc., the distillate from the top of the column is a mixture of mono- and dimethylamine, the liquid phase collected from the bottom of the column is recovered water, a side sampling port is opened near the bottom of the column, the side sampling temperature is controlled at 150~160℃, such as 150℃, 153℃, 155℃, 157℃ or 160℃, etc., the side sampling waste liquid is methanol waste liquid.

[0031] It should be noted that most of the mono- and dimethylamine obtained from dehydration can be collected and sent to the N-methylpyrrolidone synthesis reaction, while a small portion is returned to the methylamine synthesis reaction. In particular, the returned small portion of mono- and dimethylamine is mixed with the light component of the mixed amine obtained from water extraction and used as a mixed amine stream in the methylamine synthesis reaction. The non-condensable gas at the top of the dehydration tower is sent to the tail gas absorption system to recover the mixed amine. A portion of the liquid phase collected from the bottom of the tower is returned to the extraction tower as an extractant, and the remainder is sent to the park's biochemical system for treatment. The side-collected waste liquid is methanol waste liquid and is sent to the methanol recovery tower to recover methanol.

[0032] As a preferred embodiment of the present invention, the methylamine and γ-butyrolactone raw materials are pressurized to 1-3 MPaG, such as 1 MPaG, 1.5 MPaG, 2 MPaG, 2.5 MPaG, or 3 MPaG, and then mixed in a static mixer. After mixing, the materials are cooled to 70-100°C by a cross-heat exchanger and a circulating water cooler and then sent to a feed buffer tank, such as 70°C, 80°C, 90°C, or 100°C. The residence time of the materials in the feed buffer tank is controlled at 0.5-1.5 h, such as 0.5 h, 0.8 h, 1.0 h, 1.1 h, 1.3 h, or 1.5 h. The materials from the feed buffer tank are pressurized to 13-15 MPaG by a high-pressure pump, such as 13 MPaG, 13.5 MPaG, 14 MPaG, 14.5 MPaG, or 15 MPaG, to carry out the N-methylpyrrolidone synthesis reaction.

[0033] As a preferred embodiment of the present invention, in the N-methylpyrrolidone synthesis reaction, the mass ratio of the methylamine mixture to the γ-butyrolactone raw material is controlled at (0.447~0.481):1, for example, 0.447:1, 0.450:1, 0.455:1, 0.460:1, 0.465:1, 0.470:1, 0.475:1 or 0.481:1, etc.

[0034] Preferably, the reaction temperature of the N-methylpyrrolidone synthesis reaction is controlled at 340~360℃, such as 340℃, 345℃, 350℃, 355℃ or 360℃, and the residence time is controlled at 0.5~2h, such as 0.5h, 1h, 1.5h or 2h.

[0035] As a preferred technical solution of the present invention, the demethylating is carried out using a demethylating tower. The top pressure of the tower is controlled at 15~20 kPaA, for example 15 MPaA, 16 MPaA, 17 MPaA, 18 MPaA, 19 MPaA or 20 MPaA, etc. The top temperature of the tower is controlled at 58~62℃, for example 58℃, 59℃, 60℃, 61℃ or 62℃, etc. The reflux ratio is controlled at 0.8~1.5, for example 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, etc. The bottom temperature of the tower is controlled at 135~150℃, for example 135℃, 140℃, 145℃ or 150℃, etc. The distillate from the top of the tower is the liquid-phase mixed amine, and the liquid phase collected from the bottom of the tower is the crude N-methylpyrrolidone. The non-condensable gas from the top of the tower is sent to incineration treatment via a vacuum unit.

[0036] As a preferred embodiment of the present invention, the N-methylpyrrolidone purification is carried out using an NMP product column. The column top pressure is controlled at 4~6 kPaA, for example, 4 kPaA, 4.5 kPaA, 5 kPaA, 5.5 kPaA, or 6 kPaA, etc. The column top temperature is controlled at 95~105℃, for example, 95℃, 97℃, 100℃, 101℃, 103℃, or 105℃, etc. The reflux ratio is controlled at 1.5~3.0, for example, 1.5, 1.8, 2.0, 2.1, 2.3, 2.5, 2.7, or 3.0, etc. The column bottom temperature is controlled at 110~130℃, for example, 110℃, 115℃, 120℃, 125℃, or 130℃, etc. The column top distillate is the N-methylpyrrolidone product, the column bottom liquid phase is a liquid heavy component, and the column top non-condensable gas is sent to incineration treatment via a vacuum unit.

[0037] As a preferred technical solution of the present invention, the liquid phase recombination is fed to the NMP scraped film evaporator, and the operating pressure of the NMP scraped film evaporator is controlled to be consistent with that of the NMP product tower. The recovered NMP is sent to the feed buffer tank, and the residue in the reactor is heated to 70~100℃ and sent to the industrial park for further recovery of BDO. The NMP scraped film evaporator controls the purity of NMP in the residue to 40~60% by the evaporation temperature, such as 40%, 45%, 50%, 55% or 60%, etc., and the evaporation temperature is controlled at 110~140℃, such as 110℃, 120℃, 130℃ or 140℃.

[0038] It should be noted that the non-condensable gas at the top of the deammoniation tower, extraction tower, dehydration tower and methanol recovery tower described in this invention is sent to the tail gas absorption system. The tail gas absorption system is a packed absorption tower, which uses fresh methanol as the absorbent and controls the absorption temperature at 15~25℃. The methanol after absorbing the tail gas is sent to methylamine synthesis.

[0039] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0040] (1) The short-process, low-carbon emission N-methylpyrrolidone industrial chain production process described in this invention mainly uses a mixture of methylamine and γ-butyrolactone as raw materials to synthesize N-methylpyrrolidone. This not only saves the methylamine separation tower, but also solves the problem of the difficulty in selling dimethylamine. Compared with similar equipment, it effectively shortens the production process and significantly reduces the production cost of the N-methylpyrrolidone industrial chain. At the same time, the by-products generated by the production process are effectively recycled and utilized with the help of the advantages of the chemical industrial park, which greatly reduces carbon emissions. The N-methylpyrrolidone products prepared by this invention are highly competitive.

[0041] (2) The short-process, low-carbon emission N-methylpyrrolidone industrial chain production process described in this invention uses a mixture of one and two methylamines to synthesize NMP, which solves the problem that the by-product dimethylamine is difficult to sell externally, while shortening the methylamine production process and reducing the investment cost and production cost of methylamine.

[0042] (3) The short-process, low-carbon emission N-methylpyrrolidone industrial chain production process described in this invention directly uses γ-butyrolactone raw materials containing γ-butyrolactone and heavy component impurities to carry out NMP synthesis reaction, eliminating the heavy removal tower, shortening the GBL production process, and reducing GBL investment cost and production cost.

[0043] (4) The short-process, low-carbon emission N-methylpyrrolidone industrial chain production process described in this invention utilizes the advantages of the NMP industrial chain to recover by-products such as methanol, tetrahydrofuran and butanol, which greatly reduces carbon emissions, while also reducing NMP production costs and enhancing the competitiveness of NMP products. Attached Figure Description

[0044] Figure 1 This is a process flow diagram of the industrial chain production process described in this invention;

[0045] Figure 2 This is a flow chart of the methylamine synthesis process in the industrial chain production process described in Embodiment 1 of the present invention;

[0046] Figure 3 This is a flow chart of the methylamine refining process in the industrial chain production process described in Embodiment 1 of the present invention;

[0047] Figure 4This is a flow chart of the GBL synthesis process in the industrial chain production process described in Embodiment 1 of the present invention;

[0048] Figure 5 This is a flow chart of the GBL refining process in the industrial chain production process described in Embodiment 1 of the present invention;

[0049] Figure 6 This is a flow chart of the NMP synthesis process in the industrial chain production process described in Embodiment 1 of the present invention;

[0050] Figure 7 This is a flow chart of the NMP refining process in the industrial chain production process described in Embodiment 1 of the present invention;

[0051] In the diagram: 1. Methanol tank; 2. Liquid ammonia tank; 3. Mixed amine tank; 4. Azeotropic tank; 5. Methanol pressurizing pump; 6. Liquid ammonia pressurizing pump; 7. Mixed amine pressurizing pump; 8. Azeotropic tank pressurizing pump; 9. Methylamine feed static mixer; 10. Low-temperature heat exchanger; 11. Steam preheater; 12. High-temperature heat exchanger; 13. Electric heater; 14. Methylamine synthesis tower; 15. Synthesis liquid separator; 16. Deammoniation tower; 17. Deammoniation tower top condenser; 18. Azeotropic reflux tank; 19. Deammoniation tower reboiler; 20. Extraction tower; 21. Extraction tower top condenser; 22. Trimethylamine reflux tank; 23. Extraction tower reboiler; 24. Dehydration tower; 25. 26. Dehydration tower top condenser; 27. Mixed methylamine reflux tank; 28. Dehydration tower reboiler; 29. ​​Methanol recovery tower; 30. Methanol recovery tower top condenser; 31. Methanol recovery tower reboiler; 32. Extraction water heat exchanger; 33. Wastewater heat exchanger; 34. Tail gas absorption tower; 35. Tail gas absorption tower bottom pump; 36. BDO feed tank; 37. BDO pressurization pump; 38. Mixing ejector; 39. Vaporizer; 40. Superheater; 41. GBL reactor; 42. GBL heat exchanger; 43. Circulating water cooler; 44. Crude GBL tank; 45. Circulating hydrogen compressor; 46. External hydrogen supply unit. 47. Compressor; 48. Crude GBL transfer pump; 49. GBL light component removal tower; 50. GBL light component removal tower top condenser; 51. GBL light component reflux tank; 52. GBL light component reflux pump; 53. GBL light component removal tower reboiler pump; 54. GBL light component removal tower reboiler; 55. GBL product heat exchanger; 56. GBL feed tank; 57. Mixed amine feed tank; 58. GBL pressurizing pump; 59. Mixed amine pressurizing pump; 60. NMP feed static mixer; 61. NMP heat exchanger; 62. Circulating water cooler; 63. Feed buffer tank; 64. High-pressure pump; 65. Steam preheater; 66. NMP reactor; 67. Crude GBL feed tank; 68. GBL light component removal tower top condenser; 59. GBL light component removal tower top condenser; 60. GBL light component removal tower top condenser; 50. GBL light component removal tower top condenser; 61. GBL light component removal tower top condenser; 52. GBL product heat exchanger; 63. GBL feed buffer tank; 64. High-pressure pump; 65. Steam preheater; 66. NMP reactor; 77. Crude GBL feed tank; 88. GBL light component removal tower top condenser; 99. GBL product heat exchanger; 100. GBL product heat exchanger; 11. GBL product heat exchanger; 12. GBL product heat exchanger; 13. GBL product heat exchanger; 14. GBL product heat exchanger; 15. GBL product heat exchanger; 67. GBL product heat exchanger; 88. GBL product heat exchanger; 99. GBL product heat exchanger; 100. GBL product heat exchanger; 11. GBL product 67. NMP flash evaporator; 68. Demethylamine removal tower; 69. Demethylamine removal tower top condenser; 70. NMP light component reflux tank; 71. NMP light component reflux pump; 72. Demethylamine removal tower bottom circulation pump; 73. Demethylamine removal tower reboiler; 74. NMP product tower; 75. NMP product tower top condenser; 76. NMP product reflux tank; 77. NMP product reflux pump; 78. NMP product tower bottom circulation pump; 79. Scraped film evaporator; 80. Methylamine recovery tower; 81. Methylamine recovery tower top condenser; 82. Methylamine reflux tank; 83. Methylamine reflux pump; 84. Methylamine recovery tower reboiler. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0053] This invention provides a short-process, low-carbon emission production process for N-methylpyrrolidone, such as... Figure 1As shown, the production process of the industrial chain includes:

[0054] Methanol, liquid ammonia, mixed amines, and an azeotrope are mixed and heated to carry out a methylamine synthesis reaction. The resulting methylamine reaction product is deaminated to obtain an azeotrope and a deaminated heavy component. The azeotrope is returned to the methylamine synthesis reaction. The deaminated heavy component is extracted with water as an extractant to obtain a light component of the mixed amine and a mixed amine aqueous solution. The light component of the mixed amine is returned to the methylamine synthesis reaction as a raw material for the mixed amine. The mixed amine aqueous solution is dehydrated to obtain a mixture of methylamine and dimethylamine, methanol waste liquid, and recycled water. Part of the recycled water is returned to the water extraction process as an extractant, and the other part enters the park's biochemical system.

[0055] The mixture of the methylamine and γ-butyrolactone raw materials was cooled and subjected to an N-methylpyrrolidone synthesis reaction. The resulting N-methylpyrrolidone reaction product was demethylated to obtain a liquid-phase mixed amine and crude N-methylpyrrolidone. The crude N-methylpyrrolidone was then purified to obtain a liquid-phase heavy component and N-methylpyrrolidone product.

[0056] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0057] Example 1

[0058] This embodiment provides a short-process, low-carbon emission N-methylpyrrolidone industrial chain production process, the industrial chain production process including:

[0059] (1) Synthesis of methylamine:

[0060] Please see Figure 2 Methanol, liquid ammonia, mixed amine (distillate from the top of extraction tower 20 and a small portion of distillate from dehydration tower 24, i.e., a small portion of mono- and dimethylamine mixture), and azeotropic material (distillate from the top of deammoniation tower 16) are pressurized to 3.0 MPaG from methanol tank 1, liquid ammonia tank 2, mixed amine tank 3, and azeotropic material tank 4, respectively. The feed N / C ratio is controlled at 1.8:1. The pressurized material is then fed into methylamine feed static mixer 9 for mixing. The hot stream from the outlet of the methylamine synthesis tower 14 then exchanges heat with the cold stream from the outlet in the low-temperature heat exchanger 10 and the high-temperature heat exchanger 12. During normal operation, the steam preheater 11 is not in use. The hot stream is then heated to 350°C by the electric heater 13 and sent to the methylamine synthesis tower 14. The hot spot temperature of the methylamine synthesis tower 14 is controlled at 400°C. The hot stream from the outlet and the cold stream from the inlet exchange heat with the cold stream from the high-temperature heat exchanger 12 and the low-temperature heat exchanger 10, and then the temperature drops to 80°C. The hot stream is then separated into gas and liquid phases by the gas-liquid separator 15. Both the gas and liquid phases of the mixed methylamine are sent to the deammoniation tower 16.

[0061] (2) Methylamine refining:

[0062] Please see Figure 3 The gaseous and liquid mixed methylamine is fed into the deammoniation tower 16. The top pressure of the tower is controlled at 1.7 MPaG, the top temperature is controlled at 45℃, and the reflux ratio is controlled at 1.2. After the gaseous phase at the top of the tower passes through the deammoniation tower top condenser 17, the distillate, which is cooled into a liquid phase, flows to the azeotropic reflux tank 18. Part of the distillate is returned to the deammoniation tower 16, and the other part of the distillate is collected and returned to the azeotropic tank 4 of the methylamine synthesis system. The non-condensable gas goes to the tail gas absorption tower 34 to recover ammonia and mixed amine. The bottom temperature of the tower is controlled at 118℃ and heated by the deammoniation tower reboiler 19. The liquid phase collected from the bottom of the tower is sent to the extraction tower 20.

[0063] The pressure of extraction tower 20 is controlled at 0.8 MPaG, the volume ratio of extraction water to feed is controlled at 1.5, the top temperature is controlled at 79℃, and the reflux ratio is controlled at 1.1. The gas phase at the top of the tower passes through the extraction tower top condenser 21, and the distillate, which is cooled into a liquid phase, flows to the trimethylamine reflux tank 22. Part of the distillate is returned to extraction tower 20, and the other part of the distillate is collected and returned to the mixed amine tank 3 of the methylamine synthesis system. The non-condensable gas is sent to the tail gas absorption tower 34 to recover the mixed amine. The bottom temperature of the tower is controlled at 149℃ and is heated by the extraction tower reboiler 23. The liquid phase collected from the bottom of the tower is sent to the dehydration tower 24.

[0064] The pressure of the dehydration tower 24 is controlled at 0.6 MPaG, the top temperature is controlled at 55℃, and the reflux ratio is controlled at 2.2. The gas phase at the top of the tower is cooled into a liquid phase by the dehydration tower top condenser 25 and flows to the mixed methylamine reflux tank 26. Part of the distillate is returned to the dehydration tower 24, and part of the distillate is collected and returned to the mixed amine tank 3 of the methylamine synthesis system. Most of the distillate is sent to the mixed amine feed tank 56 of the NMP synthesis system. The non-condensable gas is sent to the tail gas absorption tower 34 to recover the mixed amine. The temperature of the tower bottom is controlled at 165℃ and heated by the dehydration tower reboiler 27. Part of the liquid phase collected from the tower bottom is returned to the extraction tower 20 as extraction water after heat exchange in the extraction water heat exchanger 32. The remaining liquid phase collected from the tower bottom is sent to the park's biochemical system for treatment after heat exchange in the wastewater heat exchanger 33. A side sampling port is added near the tower bottom, and the side sampling temperature is controlled at 158℃. The side sampling waste liquid is sent to the methanol recovery tower 28 to recover methanol.

[0065] The methanol recovery tower pressure is controlled at 80 kPaG, the tower top temperature is controlled at 65℃, and the reflux ratio is controlled at 11.0. The gas phase at the top of the tower passes through the methanol recovery tower top condenser 29, and the distillate, which is cooled into a liquid phase, flows to the methanol reflux tank 30. Part of the distillate is returned to the methanol recovery tower 28, and the other part of the distillate is collected and returned to the methanol tank 1 of the methylamine synthesis system. The non-condensable gas is sent to the tail gas absorption tower 34 to recover mixed amines and methanol. The tower bottom temperature is controlled at 113℃ and is heated by the methanol recovery tower reboiler 31. The liquid phase collected from the tower bottom is combined with the wastewater from the dehydration tower 24, and after heat exchange in the wastewater heat exchanger 33, it is sent to the park's biochemical system for treatment.

[0066] Please see Figure 3 The dotted box section shows that the non-condensable gas from the top of the deammoniation tower 16, extraction tower 20, dehydration tower 24, and methanol recovery tower 28 is sent to the tail gas absorption tower 34 for recovery. The tail gas absorption tower 34 is a packed absorption tower that uses fresh methanol as the absorbent and controls the absorption temperature at 18°C. The methanol after absorbing the tail gas is sent to the methanol tank 1 of the methylamine synthesis system through the tail gas absorption tower external pump 35.

[0067] (3) GBL synthesis:

[0068] Please see Figure 4 1,4-Butanediol from BDO feedstock tank 36 is atomized by BDO pressurization pump 37 and mixed with circulating hydrogen preheated by GBL heat exchanger 42. The hydrogen-to-ethanol ratio is controlled at 1:4 and the pressure is controlled at 0.3 MPaG. After mixing, it is preheated in two stages by vaporizer 39 and superheater 40 and then sent to GBL reactor 41. GBL reactor 41 is a tubular reactor with Wanhua's self-developed catalyst inside the tubes. The reaction cold point temperature is controlled at 185℃. After the hot stream from GBL reactor 41 and circulating hydrogen exchange heat in GBL heat exchanger 42, it is further cooled by circulating water cooler 43. Most of the gas phase obtained from cooling is returned as circulating hydrogen by pressurization through circulating hydrogen compressor 45. A small part is pressurized by external hydrogen compressor 46 and sent to washing tower for further treatment and utilization in the park. The liquid phase obtained from cooling is GBL crude product, which is sent to GBL light product removal tower 48 by crude GBL transfer pump 47.

[0069] (4) GBL Refined:

[0070] Please see Figure 5 The crude GBL product is sent to the GBL light component removal tower 48, where the top pressure is controlled at 12 kPaA, the top temperature is controlled at 80°C, and the reflux ratio is controlled at 7.0. The gas phase at the top of the tower passes through the GBL light component removal tower top condenser 49 and is cooled into a liquid phase. The distillate flows to the GBL light component reflux tank 50 and passes through the GBL light component reflux pump 51. Part of the distillate is returned to the GBL light component removal tower 48, and part of the liquid phase is collected and sent to the industrial park for further recovery of tetrahydrofuran (THF) and butanol. The non-condensable gas is absorbed by the vacuum unit circulating liquid and then sent to incineration. The tower bottom temperature is controlled at 134°C. The tower bottom material is collected through the GBL light component removal tower bottom circulating pump 52. Part of it is heated by the GBL light component removal tower reboiler 53 and then returned to the GBL light component removal tower 48. The other part is heat-exchanged by the GBL product heat exchanger 54 and then sent to the GBL raw material tank 55 of the NMP synthesis system.

[0071] (5) NMP synthesis:

[0072] Please see Figure 6The raw materials in the GBL raw material tank 55 and the mixed methylamine tank 56 are pressurized to 1.6 MPaG by the GBL pressurizing pump 57 and the mixed amine pressurizing pump 58, respectively, and then enter the NMP static mixer 59 for mixing. The mass ratio of mono- and di-mixed methylamine to GBL is controlled at 0.465:1. After mixing, the material exchanges heat with the material in the feed buffer tank 62 through the NMP material heat exchanger 60, and then is cooled to 85°C by the circulating water cooler 61 and sent to the feed buffer tank 62. The residence time of the material in the feed buffer tank 62 is controlled at 1 hour. The material is pressurized to 13.9 MPaG by the high-pressure pump 63, and after heat exchange by the NMP material heat exchanger 60 and heating by the steam preheater 64, it is sent to the NMP reactor 65. The NMP reactor 65 controls the reaction temperature at 355°C and the residence time at 2 hours by the heat transfer oil. The crude NMP product generated by the reaction enters the crude NMP flash tank 66 for flash evaporation. Both the gaseous and liquid phase materials are sent to the demethylamine removal tower 67.

[0073] (6) NMP refining:

[0074] Please see Figure 7 The crude NMP product is sent to the demethylating tower 67, where the top pressure is controlled at 20 kPaA, the top temperature at 62°C, and the reflux ratio at 1.0. The vapor phase at the top of the tower passes through the demethylating tower top condenser 68, and the distillate, cooled into a liquid phase, flows to the NMP light component reflux tank 69. Through the NMP light component reflux pump 70, part of the distillate is returned to the demethylating tower 67, and the other part is collected and sent to the methylating recovery tower 80 for simple methanol and water removal. The non-condensable gas at the top of the demethylating tower 67 is absorbed by the circulating liquid of the vacuum unit and then sent for incineration. The liquid phase collected from the bottom of the demethylating tower 67 is pressurized by the demethylating tower bottom circulating pump 71, and part of it is heated through the demethylating tower reboiler 72, where the bottom temperature is controlled at 150°C. The other part is collected and sent to the NMP product tower 73.

[0075] The pressure of NMP product column 73 is controlled at 4 kPa, the top temperature at 95°C, and the reflux ratio at 1.8. The vapor phase at the top of the column passes through the NMP product column top condenser 74, and the distillate, cooled into a liquid phase, flows to the NMP product reflux tank 75. Through the NMP product reflux pump 76, a portion of the distillate is returned to the NMP product column 73, and the remaining portion is collected as NMP product. If the analysis is satisfactory, it is directly sent to the NMP product tank for collection; if the analysis is unsatisfactory, it is sent to the feed buffer tank 62. Non-condensable gases are absorbed by the circulating liquid in the vacuum unit and then sent for incineration. The bottom liquid... The NMP product tower is pressurized by the circulating pump 78. Part of it is heated by the reboiler 77 and returned to the NMP product tower 73, with the tower bottom temperature controlled at 130°C. The other part is collected and sent to the scraped film evaporator 79. The operating pressure of the scraped film evaporator 79 is the same as that of the NMP product tower 73. The NMP purity of the residue in the scraped film evaporator 79 is controlled to 50% by the evaporation temperature, which is controlled at 120°C. The recovered NMP is sent to the feed buffer tank 62. The residue is heated to 70~100°C and sent to the industrial park for further BDO recovery.

[0076] The vapor phase at the top of the methylamine recovery tower 80 is cooled into a liquid phase by the condenser 81 at the top of the methylamine recovery tower and flows to the methylamine reflux tank 82. After being pressurized by the methylamine reflux pump 83, part of it is returned to the methylamine recovery tower 80, and the other part is sent to the deammoniation tower 16 for further purification. The non-condensable gas is absorbed by the circulating liquid of the vacuum unit and then sent for incineration. The liquid phase collected from the bottom of the methylamine recovery tower 80 is partially heated by the reboiler 84 of the methylamine recovery tower, and the other part is sent to the methanol recovery tower 28 to be mixed with methanol waste liquid to recover methanol.

[0077] It should be noted that steps (1) and (2) are in a specific order, namely, methylamine synthesis and methylamine purification are carried out in sequence. Steps (3) and (4) are in a specific order, namely, GBL synthesis and GBL purification are carried out in sequence. However, steps (1) and (3) are not in a specific order.

[0078] In this embodiment, the purity, reaction yield and key impurity content of the mono- and dimethylamine obtained in steps (1) and (2) are characterized, the purity, reaction yield and key impurity content of the de-light GBL (i.e., γ-butyrolactone raw material containing γ-butyrolactone and heavy component impurities) obtained in steps (3) and (4) are characterized, and the purity, reaction yield and key impurity content of the NMP product obtained in steps (5) and (6) are characterized. The specific characterization results are shown in Table 1.

[0079] Table 1

[0080]

[0081] Comparative Example 1

[0082] This comparative example provides a production process for the N-methylpyrrolidone industrial chain. Compared with Example 1, the only difference is that in step (2) methylamine refining, the bottom liquid of the deammoniation tower 16 is sent to a distillation tower to separate methanol. The separated mixed amine is directly sent to the mixed amine feed tank 56 of the NMP synthesis system and used directly as the mixed amine feedstock for the NMP synthesis reaction. It should be noted that because the bottom liquid of the deammoniation tower contains a lot of water and methanol, in order to deduct the influence of water and methanol, the mass ratio of the first, second, and third mixed methylamines to GBL is increased to 0.626:1.

[0083] In this comparative example, the purity, reaction yield and key impurity content of the mixed methylamine obtained in steps (1) and (2) were characterized, the purity, reaction yield and key impurity content of the de-light GBL (i.e., γ-butyrolactone raw material containing γ-butyrolactone and heavy component impurities) obtained in steps (3) and (4) were characterized, and the purity, reaction yield and key impurity content of the NMP product obtained in steps (5) and (6) were characterized. The specific characterization results are shown in Table 2.

[0084] Table 2

[0085]

[0086] Comparing Example 1 with Comparative Example 1, it can be seen that the reaction rate of trimethylamine with GBL is relatively slow, resulting in a large amount of GBL residue in the reaction product. Since GBL and NMP have similar boiling points, almost all of GBL is transferred to the NMP product, causing a decrease in the purity of the NMP product, which cannot meet the requirements for electronic grade.

[0087] This invention provides a short-process, low-carbon emission N-methylpyrrolidone (NMP) industrial chain production process. It focuses on the reaction of dimethylamine and γ-butyrolactone (GBL) feedstock to synthesize NMP, eliminating the need for a methylamine separation tower and resolving the difficulty of selling dimethylamine externally. Furthermore, it directly uses GBL feedstock containing GBL and heavy component impurities for NMP synthesis, eliminating the need for a heavy component removal tower, shortening the GBL production process, and reducing GBL investment and production costs. Moreover, leveraging the advantages of the NMP industrial chain, it recovers byproducts such as methanol, tetrahydrofuran, and butanol, significantly reducing carbon emissions and lowering NMP production costs, thus enhancing the competitiveness of NMP products. Compared to similar equipment, this invention effectively shortens the production process, significantly reduces the production cost of the NMP industrial chain, and allows for the effective recycling of byproducts generated during production, taking advantage of the chemical industrial park, further reducing carbon emissions. The NMP product prepared by this invention is highly competitive.

[0088] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0089] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0090] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction, in order to avoid unnecessary repetition. The present invention will not describe the various possible combinations separately.

[0091] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, and should also be considered as controlled within the scope disclosed in the present invention.

Claims

1. A process for producing N-methylpyrrolidone that eliminates the need for a methylamine separation tower, characterized in that, The production process includes: Methanol and liquid ammonia are mixed and heated to carry out a methylamine synthesis reaction. The methylamine reaction product is then subjected to deammoniation, water extraction, and dehydration to obtain mixed methylamine, methanol waste liquid, and recycled water. The methylamine reaction product is deaminated to obtain an azeotrope and a deaminated heavy component; the deaminated heavy component is extracted with water as an extractant to obtain a mixed amine light component and a mixed amine aqueous solution; the mixed amine aqueous solution is dehydrated to obtain the mono- and di-mixed methylamine, methanol waste liquid and recycled water; most of the mono- and di-mixed methylamine obtained from dehydration is collected and sent to the N-methylpyrrolidone synthesis reaction, while a small portion is returned to the methylamine synthesis reaction; The azeotrope and the light component of the mixed amine are returned to the methylamine synthesis reaction and used as raw materials to mix with methanol and liquid ammonia; part of the recycled water is returned to the aqueous extraction process as an extractant, and the other part enters the park's biochemical system. The methylamine and γ-butyrolactone raw materials were pressurized and mixed in a static mixer. After mixing, the materials were cooled and sent to a feed buffer tank. After being pressurized and heated, N-methylpyrrolidone synthesis reaction was carried out. The residence time of the N-methylpyrrolidone synthesis reaction was controlled at 0.5~2h. The obtained N-methylpyrrolidone reaction product was demethylated to obtain liquid-phase mixed amine and crude N-methylpyrrolidone. The crude N-methylpyrrolidone was purified to obtain liquid-phase heavy components and N-methylpyrrolidone product.

2. The production process according to claim 1, characterized in that, The γ-butyrolactone raw material was obtained by the following preparation method: 1,4-Butanediol is mixed with recycled hydrogen and preheated to carry out the γ-butyrolactone synthesis reaction. The resulting γ-butyrolactone reaction product is cooled to obtain a gaseous product and a crude liquid product. A portion of the gaseous product is returned as recycled hydrogen, and the other portion is recycled. The crude liquid product is purified to remove light components and obtain light component impurities and the γ-butyrolactone raw material. The light component impurities include tetrahydrofuran and butanol, and the γ-butyrolactone raw material contains γ-butyrolactone and heavy component impurities.

3. The production process according to claim 2, characterized in that, 1,4-Butanediol is atomized under high pressure and then mixed with preheated circulating hydrogen. The hydrogen-to-ethanol ratio is controlled at 12-16 and the pressure is controlled at 0.3-0.5 MPaG.

4. The production process according to claim 2, characterized in that, The cold point temperature of the γ-butyrolactone synthesis reaction is controlled at 180~210℃.

5. The production process according to claim 2, characterized in that, The light component removal and purification process is carried out using a GBL light component removal tower. The tower top pressure is controlled at 10~15 kPaA, the tower top temperature is controlled at 75~90℃, the reflux ratio is controlled at 5.0~15.0, and the tower bottom temperature is controlled at 130~140℃. The bottom liquid is γ-butyrolactone feedstock containing γ-butyrolactone and heavy component impurities. The top distillate is the light component impurities and is sent to the industrial park for further recovery of tetrahydrofuran and butanol.

6. The production process according to claim 1, characterized in that, The methanol waste liquid enters the methanol recovery tower for treatment. The recovered methanol obtained from the top of the tower is returned to the methylamine synthesis reaction as raw material methanol, and the wastewater obtained from the bottom of the tower enters the park's biochemical system.

7. The production process according to claim 6, characterized in that, The methanol recovery tower pressure is controlled at 50~100 kPaG, the tower top temperature is controlled at 60~80℃, the reflux ratio is controlled at 10.0~20.0, and the tower bottom temperature is controlled at 110~115℃.

8. The production process according to claim 1, characterized in that, Methanol and liquid ammonia are mixed, pressurized to 2.6~3.2 MPaG, and heated to 320~360℃.

9. The production process according to claim 1, characterized in that, The feed N / C ratio for the methylamine synthesis reaction is 1.2~2.2:

1.

10. The production process according to claim 1, characterized in that, The reaction temperature for the methylamine synthesis reaction is controlled at 390~420℃.

11. The production process according to claim 1, characterized in that, The methylamine and γ-butyrolactone raw materials are pressurized to 1-3 MPaG and mixed in a static mixer. After mixing, the materials are cooled to 70-100°C and sent to a feed buffer tank. The residence time of the materials in the feed buffer tank is controlled at 0.5-1.5 h. The materials from the feed buffer tank are pressurized to 13-15 MPaG to carry out the N-methylpyrrolidone synthesis reaction.

12. The production process according to claim 11, characterized in that, In the N-methylpyrrolidone synthesis reaction, the mass ratio of the methylamine and γ-butyrolactone raw material is controlled at (0.447~0.481):

1.

13. The production process according to claim 1, characterized in that, The reaction temperature for the synthesis of N-methylpyrrolidone is controlled at 340~360℃.

14. The production process according to claim 1, characterized in that, The demethylating process is carried out using a demethylating column, with the top pressure controlled at 15~20 kPaA, the top temperature controlled at 58~62℃, the reflux ratio controlled at 0.8~1.5, and the bottom temperature controlled at 135~150℃. The distillate from the top of the column is the liquid-phase mixed amine, and the liquid phase collected from the bottom of the column is the crude N-methylpyrrolidone.

15. The production process according to claim 1, characterized in that, The purification of N-methylpyrrolidone is carried out using an NMP product column, with the top pressure controlled at 4~6 kPaA, the top temperature controlled at 95~105℃, the reflux ratio controlled at 1.5~3.0, and the bottom temperature controlled at 110~130℃. The distillate from the top of the column is the N-methylpyrrolidone product, and the liquid phase collected from the bottom of the column is the heavy liquid component.

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