Continuous production method for preparing N-methyl pyrrolidone through serial interstage feeding catalytic reaction

Abstract

The invention belongs to the field of fine chemical engineering, and particularly relates to a continuous production method for preparing NMP (N-Methyl Pyrrolidone) through a serial inter-stage feeding catalytic reaction, which comprises the following steps of: reacting gamma-butyrolactone and monomethylamine through a three-stage reactor, and performing flash evaporation, deamination and rectification to obtain NMP (N-Methyl Pyrrolidone); wherein the process of the gamma-butyrolactone and the monomethylamine passing through the three-stage reactor is as follows: the gamma-butyrolactone is continuously introduced into the first reactor, the introduction amount of the monomethylamine in the first reactor is 30%-50% of the total amount, and the gamma-butyrolactone and the monomethylamine react for 5-15 minutes at the temperature of 180-210 DEG C under the pressure of 7.8-8 MPa; the material flow obtained in the first reactor is introduced into a second reactor, the introduction amount of monomethylamine in the second reactor is 20%-40% of the total amount, and a reaction is carried out for 1-2 hours at 210-230 DEG C under 7.6-7.8 MPa; and introducing the material flow obtained in the second reactor into a third reactor, adding the residual monomethylamine into the third reactor, and reacting at 230-270 DEG C under 7.4-7.6 MPa for 1-1.2 hours. According to the method, the purity of NMP can reach 99% or above, the energy consumption is reduced, and the energy efficiency and sustainability of the process are improved.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and in particular relates to a continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series inter-stage feeding. Background Art

[0002] N-Methylpyrrolidone (NMP) is a colorless, transparent, non-proton transfer liquid with a slight ammonia smell. It has excellent solubility and can be completely mixed with various solvents such as ethanol, acetaldehyde, ketones, aromatic hydrocarbons, water, etc. It has good chemical stability and high thermal stability, low volatility, and weak toxicity. Due to its excellent properties, NMP is widely used in many fields, including lithium batteries, chemical industry, semiconductors, pesticides, and dyes. Among them, the application scale of NMP in the lithium battery industry is the largest. In the synthesis of NMP, most manufacturers use 1,4-butanediol (BDO) dehydrogenation to produce γ-butyrolactone (GBL), and then amination condensation with monomethylamine to produce NMP. This preparation process is both efficient and controllable, providing a reliable method for the industrial production of NMP.

[0003] The traditional synthesis method of NMP mainly includes the condensation reaction of γ-butyrolactone and monomethylamine aqueous solution, but this reaction usually needs to be carried out under high temperature and high pressure conditions, and is accompanied by the generation of byproduct water, the reaction rate is slow, and the product selectivity is low. In addition, the traditional process usually requires the use of strong acid or strong base as a catalyst, which not only corrodes the equipment and increases production costs, but also brings problems of waste liquid treatment and environmental pollution. However, there are two major problems with the traditional process: first, the water in the methylamine aqueous solution does not participate in the reaction, but requires heating, increasing pressure, cooling, and reducing pressure, which increases energy consumption; second, the NMP condensation reaction is a slow process, requiring a large reactor and a long residence time. The presence of water further increases the reactor volume and manufacturing difficulty, resulting in high energy consumption, limited production scale and other problems. In order to overcome the various shortcomings in the traditional NMP synthesis process, under the condition of a composite carrier catalyst, the selection of an efficient continuous production process has become a key strategy to improve reaction efficiency, product selectivity and reduce energy consumption. Summary of the invention

[0004] In view of the problems and shortcomings in the prior art, the object of the present invention is to provide a continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series inter-stage feeding.

[0005] Based on the above purpose, the present invention adopts the following technical solution:

[0006] The present invention provides a continuous production method for preparing N-methylpyrrolidone by cascade interstage feeding catalytic reaction, wherein γ-butyrolactone and a monomethylamine aqueous solution are reacted in a three-stage reactor, and then flashed, deaminized and distilled to obtain N-methylpyrrolidone; wherein the specific process of the reaction of γ-butyrolactone and a monomethylamine aqueous solution in the three-stage reactor is as follows:

[0007] (1) γ-butyrolactone is continuously introduced into a first reactor uniformly distributed with a catalyst, an aqueous monomethylamine solution is introduced into the first reactor in an amount of 30% to 50% of the total amount of the aqueous monomethylamine solution, and an amount of the catalyst is 2% to 2.5% of the total mass of the catalyst, and the reaction is carried out at 180 to 210° C. and 7.8 to 8 MPa for 5 to 15 minutes;

[0008] (2) then passing the stream obtained from the first reactor into a second reactor, adding a monomethylamine aqueous solution in an amount of 20% to 40% of the total amount of the monomethylamine aqueous solution and a catalyst in an amount of 1.5% to 2% of the total mass of the catalyst to the second reactor, and continuing to react with unreacted γ-butyrolactone at 210 to 230° C. and 7.6 to 7.8 MPa for 1 to 2 hours;

[0009] (3) The stream obtained from the second reactor is passed into the third reactor, and the remaining monomethylamine aqueous solution is added to the third reactor. The amount of catalyst used is 1% to 1.5% of the total mass of the catalyst. The reaction is carried out at 230 to 270° C. and 7.4 to 7.6 MPa for 1 to 1.2 hours.

[0010] Preferably, the catalyst uses Y molecular sieve / γ-Al2O3 as a composite carrier and is loaded with a metal active component Cu; the preparation steps of the catalyst are: evenly disperse the active component Cu(NO3)2·3H2O in deionized water, add Y molecular sieve and γ-Al2O3 composite carrier after complete dissolution, stir to fully mix, and soak for 12 hours at room temperature. Then, dry at 110°C for 12 hours, and calcine at 560°C in an air atmosphere for 4 hours. The prepared catalyst is named Cu x / Y molecular sieve / γ-Al2O3 catalyst, wherein x (x=0.2, 0.4, 0.6 and 0.8) represents the ratio of the mass of Cu to the mass of γ-Al2O3 / Y molecular sieve composite carrier.

[0011] Preferably, based on the total weight of the catalyst, the content of the metal active component Cu is 0.2% to 0.8%.

[0012] More preferably, based on the total weight of the catalyst, the content of the metal active component Cu is 0.4%.

[0013] Preferably, the mass percentage concentration of the monomethylamine aqueous solution is 40% to 60%.

[0014] More preferably, the mass percentage concentration of the monomethylamine aqueous solution is 50%.

[0015] Preferably, the mass ratio of the total amount of γ-butyrolactone and the monomethylamine aqueous solution is 1:1-2.

[0016] More preferably, the mass ratio of the total amount of γ-butyrolactone and the monomethylamine aqueous solution is 1:1.3.

[0017] Preferably, the amount of the catalyst used is 1% to 10% of the total mass of the γ-butyrolactone and monomethylamine aqueous solution.

[0018] More preferably, the amount of the catalyst used is 2% to 5% of the total mass of the γ-butyrolactone and monomethylamine aqueous solution.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention synthesizes NMP by passing γ-butyrolactone and monomethylamine aqueous solution through three tubular reactors in sequence under the action of Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst. The temperature of each reactor is gradually increased, and the pressure is gradually reduced. A portion of monomethylamine aqueous solution is added in each stage, and the catalyst is evenly distributed in the tubular reactor in the first reaction. By dividing into three different reactors for step-by-step reaction, the violent reaction and heat release problems that may be caused by one-time feeding can be avoided, the accumulation of unreacted raw materials is reduced, and the stability and safety of the reaction are improved. Moreover, under high temperature and low pressure conditions, γ-butyrolactone is almost completely converted into NMP, and the discharge NMP mixture of the reactor is flashed through a flash tank, and the vapor and liquid phases obtained by flashing are then deaminized, dehydrated, and distilled to obtain the NMP product, and the purity can reach more than 99%. This process significantly reduces energy consumption, thereby improving the energy efficiency and sustainability of the process.

[0021] (2) The advantage of the Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst is that its synergistic effect can significantly improve the catalytic performance. The high specific surface area and acidic properties of the Y molecular sieve help to improve the selectivity of the target product while inhibiting the occurrence of side reactions. γ-Al2O3 provides excellent thermal stability and mechanical strength, ensuring that the catalyst is suitable for complex reaction conditions. In addition, the good dispersion of copper active centers improves the catalytic activity, and the structural design of the composite carrier also enhances the resistance to carbon deposition and poisoning, prolongs the service life of the catalyst and reduces the cost, making it suitable for the multi-step process requirements of the NMP synthesis reaction.

[0022] (3) In the continuous production of the present invention, the reactor design is more compact, the materials can complete the reaction in a shorter time, and the energy loss of heating and cooling is reduced. By accurately controlling the amount of catalyst used and the reaction conditions, the continuous production process can effectively reduce the side reactions, and the alkane ketone and amide impurities in the product are significantly reduced, so that the conversion rate of γ-butyrolactone is ≥99%, and the selectivity of NMP is ≥99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a schematic flow diagram of a continuous production method for preparing N-methylpyrrolidone by a series of inter-stage feeding catalytic reactions.

[0024] In the figure, R1 is the first reactor; R2 is the second reactor; R3 is the third reactor; E4 is a flash tank; T5 is an amine removal tower; T6 is a dehydration tower; and T7 is a distillation tower. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments in combination with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] (I) Study on the effect of Cu loading on conversion rate and selectivity

[0027] Example 1

[0028] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0029] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 40% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst with a Cu element content of 0.2% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0030] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0031] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0032] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 98%, and the selectivity of NMP reaches 98.2%. The specific experimental data results are shown in Table 1.

[0033] Example 2

[0034] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0035] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 40% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst with a Cu content of 0.4% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0036] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0037] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0038] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 99.4%, and the selectivity of NMP reaches 99.5%. The specific experimental data results are shown in Table 1.

[0039] Example 3

[0040] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0041] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 40% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst with a Cu content of 0.6% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0042] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0043] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0044] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 98.9%, and the selectivity of NMP reaches 98.1%. The specific experimental data results are shown in Table 1.

[0045] Example 4

[0046] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0047] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 40% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst with a Cu content of 0.8% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0048] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0049] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0050] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 96.8%, and the selectivity of NMP reaches 95.6%. The specific experimental data results are shown in Table 1.

[0051] Table 1 Effect of Cu loading on conversion and selectivity

[0052]

[0053] As shown in Table 1, by changing the Cu loading of the catalyst, we found that when the Cu loading was 0.4%, the catalyst performed best, that is, the conversion rate of the reactants and the selectivity of the target product NMP reached the highest values, and the amount of by-products generated was the least. Although high loading (such as 0.6%, 0.8%) increased the Cu content, it may increase the side reactions due to particle agglomeration or oversaturation of active sites, thereby reducing the selectivity and conversion rate.

[0054] (II) Study on the effect of mass percentage concentration of monomethylamine aqueous solution on conversion rate and selectivity

[0055] Example 5

[0056] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0057] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 50% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst with a Cu content of 0.4% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0058] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 2% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0059] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0060] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 99.7%, and the selectivity of NMP reaches 99.8%. The specific experimental data results are shown in Table 2.

[0061] Example 6

[0062] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0063] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 60% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve / γ-Al2O3 composite carrier catalyst with a Cu content of 0.4% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0064] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0065] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0066] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 98.3%, and the selectivity of NMP reaches 98.7%. The specific experimental data results are shown in Table 2.

[0067] Table 2 Effect of mass percentage concentration of monomethylamine aqueous solution on conversion rate and selectivity

[0068]

[0069]

[0070] As shown in Table 2, by changing the mass percentage concentration of monomethylamine aqueous solution, we found that when the mass percentage concentration is 50%, the reaction performance is the best, the selectivity of the target product NMP reaches 99.8%, the conversion rate of the reactants also reaches 99.7%, and the amount of by-products generated is the least; when the mass percentage concentration of monomethylamine aqueous solution is 40%, although it can maintain a high selectivity and conversion rate, the by-products are relatively more; and when the mass percentage concentration is increased to 60%, the conversion rate decreases significantly, the by-products of alkanones and amides increase significantly, and the purity of the target product decreases. Therefore, using 50% mass percentage concentration as the optimization condition can achieve the best reaction performance and target product yield.

[0071] (III) Study on the effect of different catalyst carriers on conversion rate and selectivity

[0072] Comparative Example 1

[0073] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0074] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 50% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-Y molecular sieve catalyst with a Cu content of 0.4% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0075] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0076] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0077] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 98.6%, and the selectivity of NMP reaches 98.2%. The specific experimental data results are shown in Table 3.

[0078] Comparative Example 2

[0079] A continuous production method for preparing N-methylpyrrolidone by cascading interstage feeding catalytic reaction, wherein γ-butyrolactone and monomethylamine aqueous solution react in a three-stage reactor, and then flash, deaminize, and distill to obtain N-methylpyrrolidone, and the specific steps are as follows:

[0080] (1) In the first reactor R1, γ-butyrolactone is continuously introduced, the reaction temperature is controlled at 200°C, and the pressure is 7.8MPa. In this stage, a monomethylamine aqueous solution with a mass percentage concentration of 50% is added, the amount of monomethylamine aqueous solution introduced is 40% of the total amount of monomethylamine aqueous solution, the total amount of monomethylamine aqueous solution is 500g, the mass ratio of γ-butyrolactone and the total amount of monomethylamine aqueous solution is controlled at 1:1.3, and a Cu-γ-Al2O3 catalyst with a Cu content of 0.4% is added and evenly distributed in the reactor, and the amount of catalyst is 2% of the total mass of the catalyst to ensure that the reactants fully contact the catalyst surface and improve the reaction efficiency. Under this reaction condition, γ-butyrolactone and monomethylamine aqueous solution undergo a preliminary condensation reaction, and the reaction residence time is 10min;

[0081] (2) Then, the logistics produced by the first reactor R1 enters the second reactor R2. At this stage, the reaction temperature is increased to 220°C and the pressure is 7.6MPa. At this time, the amount of monomethylamine aqueous solution is 30% of the total amount of monomethylamine aqueous solution, and the amount of catalyst is 1.5% of the total mass of the catalyst, which continues to react with the unreacted γ-butyrolactone, so that the reaction rate is further improved. In this stage, the temperature and pressure are adjusted to effectively promote the progress of the reaction, and the reaction residence time is 1.5h;

[0082] (3) In the third reactor R3, the reaction temperature continues to rise to 250°C, while the pressure is reduced to 7.4 MPa. At this time, the remaining monomethylamine aqueous solution is added to the third reactor R3, the catalyst dosage is 1.5% of the total mass of the catalyst, the reaction residence time is 1 hour, and an NMP product mixture is obtained;

[0083] (4) The mixed stream is flashed in the flash tank E4. The vapor and liquid phases obtained by flashing are: the vapor phase is passed through the deamine tower T5 and the dehydration tower T6 to recover monomethylamine for further use; the liquid phase is passed through the deamine tower T5 and the distillation tower T7 to obtain the NMP product. The conversion rate of γ-butyrolactone reaches 97.8%, and the selectivity of NMP reaches 97.9%. The specific experimental data results are shown in Table 3.

[0084] Table 3 Effect of different catalyst carriers on conversion and selectivity

[0085]

[0086] As shown in Table 3, by changing the catalyst carrier, we found that the composite carrier significantly improved the performance of the catalyst. When the composite carrier was used, the conversion rate increased from 98.6% and 97.8% of the single carrier to 99.7%, the NMP selectivity increased from 98.2% and 97.9% to 99.8%, and the amount of alkane and amide by-products generated was greatly reduced. Therefore, the composite carrier showed significant advantages in improving catalytic activity, selectivity and reducing by-product generation.

Claims

1. A continuous production method for preparing N-methylpyrrolidone by catalytic reaction of feeding materials in series, characterized in that: The γ-butyrolactone and the monomethylamine aqueous solution are reacted in a three-stage reactor, and then flashed, deaminized, and distilled to obtain N-methylpyrrolidone; wherein the specific process of the γ-butyrolactone and the monomethylamine aqueous solution reacting in the three-stage reactor is as follows: (1) γ-butyrolactone is continuously introduced into a first reactor uniformly distributed with a catalyst, an aqueous monomethylamine solution is introduced into the first reactor in an amount of 30% to 50% of the total amount of the aqueous monomethylamine solution, and an amount of the catalyst is 2% to 2.5% of the total mass of the catalyst, and the reaction is carried out at 180 to 210° C. and 7.8 to 8 MPa for 5 to 15 minutes; (2) then passing the stream obtained from the first reactor into the second reactor, adding a monomethylamine aqueous solution in an amount of 20% to 40% of the total amount of the monomethylamine aqueous solution and a catalyst in an amount of 1.5% to 2% of the total mass of the catalyst into the second reactor, and continuing to react with the unreacted γ-butyrolactone at 210 to 230° C. and 7.6 to 7.8 MPa for 1 to 2 hours; (3) The stream obtained from the second reactor is passed into the third reactor, and the remaining monomethylamine aqueous solution is added to the third reactor. The amount of catalyst used is 1% to 1.5% of the total mass of the catalyst. The reaction is carried out at 230 to 270° C. and 7.4 to 7.6 MPa for 1 to 1.2 hours.

2. The continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series interstage feeding according to claim 1, characterized in that: The catalyst uses Y molecular sieve / γ-Al2O3 as a composite carrier and is loaded with a metal active component Cu.

3. The continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series interstage feeding according to claim 2, characterized in that: Based on the total weight of the catalyst, the content of the metal active component Cu is 0.2% to 0.8%.

4. The continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series interstage feeding according to claim 1, characterized in that: The mass percentage concentration of the monomethylamine aqueous solution is 40% to 60%.

5. The continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series interstage feeding according to claim 1, characterized in that: The mass ratio of the total amount of the γ-butyrolactone and the monomethylamine aqueous solution is 1:1-2.

6. The continuous production method for preparing N-methylpyrrolidone by catalytic reaction of series interstage feeding according to claim 1, characterized in that: The amount of the catalyst used is 1% to 10% of the total mass of the gamma-butyrolactone and monomethylamine aqueous solution.

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