Method for preparing energy-saving pyrrolidinone

Abstract

The present invention relates to the technical field of the preparation of pyrrolidinone. Disclosed is a method for preparing energy-saving pyrrolidinone. The method comprises: mixing γ-butyrolactone with an organic amine or ammonia water, and sequentially passing the mixture through an I-stage reactor, an II-stage reactor, a reactor higher than stage II and a laminar flow reactor, so as to obtain a hot material; and sequentially passing the obtained material through the I-stage reactor in step 1, a condenser and a constant-pressure tank, so as to obtain pyrrolidinone. The condensation process, in which γ-butyrolactone and an organic amine or ammonia are used, is a typical heat release process; in addition, accurate thermodynamic parameters are obtained on the basis of basic research, so as to optimize and simulate the process and fully utilize the heat released by the reaction, such that the reaction system does not need an external supplementary heat source, can also generate heat for external use, and can further save on circulating water, thereby greatly reducing the amount of circulating water.

Description

A method for preparing energy-saving pyrrolidone Technical Field

[0001] The present invention relates to the technical field of pyrrolidone preparation, in particular to a method for preparing energy-saving pyrrolidone. Background Art

[0002] Pyrrolidone products include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-octyl-2-pyrrolidone, etc. At the same time, its main industrial application products are 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0003] 2-Pyrrolidone (2-pyrrolidinone), also known as α-pyrrolidone, is a lactam compound with a five-membered heterocyclic ring structure, also known as γ-butyrolactam. Its molecular formula is C₄H₄NO, and its molecular mass is 85.12. Several industrial methods exist for producing 2-pyrrolidone, including the γ-butyrolactone amination method, the DMS method, and the maleic anhydride hydrogenation method. However, the primary methods used are the γ-butyrolactone amination method and the maleic anhydride or succinic acid hydrogenation method.

[0004] N-methyl-2-pyrrolidinone (NMP), also known as N-methylpyrrolidone, methylpyrrolidone, or NMP, has a molecular formula of C5H9NO and a relative molecular mass of 99.13. It is an important derivative of γ-butyrolactone. At room temperature, NMP is a colorless, transparent liquid with a slight ammoniacal odor. It is a highly polar, chemically and thermally stable solvent with a high boiling point. It is completely miscible with water, lower alcohols, ether, ketones, ethyl acetate, chloroform, and benzene. Unsaturated hydrocarbons such as alkynes, dienes, and alkenes have higher solubility in NMP than saturated hydrocarbons. Furthermore, NMP can dissolve a variety of polymers, making it a high-performance polar organic solvent and an extraction and separation solvent. Numerous methods exist for synthesizing NMP, including the succinonitrile method, the methyl 4-oxybutyrate method, and the 1,4-butanedioic acid method. However, the only industrially available method for its production is the condensation of γ-butyrolactone with methylamine. The production process of N-methyl-2-pyrrolidone is mainly the condensation method of γ-butyrolactone and ethylamine.

[0005] Therefore, the mainstream production process for pyrrolidone is the condensation of γ-butyrolactone with organic amines or ammonia. Taking NMP as an example, the condensation of γ-butyrolactone with methylamine is a classic NMP production technology developed by BASF in Germany in the early years and has been used for many years. The reaction process is as follows:

[0006]

[0007] For example, Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, Volume A22, pages 458-459; and "1,4-Butanediol, Tetrahydrofuran and Their Industrial Derivatives", Chemical Industry Press, 2013, Chapter 4 describes: γ-butyrolactone, methylamine and water are reacted in the absence of a catalyst at 250-330°C, a pressure of about 6-14 MPa, in a liquid phase, and for a residence time of about 1.5-3 h to obtain NMP with high conversion and high selectivity, and a high-purity product is obtained by distillation and dehydration.

[0008] Various studies have been conducted both domestically and internationally on pyrrolidone synthesis reaction systems, employing multi-stage series-connected autoclave reactors, batch processes, and plug-flow tubular reactors. For example, Winnacker and Küchler ("Chemische Technologie," 4th edition, 1982, Vol. 6) mention on page 99, lines 5-9 that γ-butyrolactam (2-pyrrolidone) is prepared from GBL by complete reaction with liquid ammonia at 270° C. and approximately 120 bar (selectivity: 94 mol%) (DE-A-1795007), and that NMP is formed in a similar reaction with methylamine.

[0009] For example, the nitrogen constant pressure process proposed by Chinese scientists Yang Yuanyi et al., as described in CN1104635, utilizes a pipeline reactor with an operating temperature of 220-290°C, a residence time of 1-3 hours, and a reaction pressure of 6.0 MPa or higher. This continuous operation mode is easy to operate and has good results when applied on a certain scale. CN100447132 also discloses a method for the continuous preparation of N-methyl-2-pyrrolidone (NMP), characterized by operating at higher temperatures and pressures to achieve high yields and short residence times. Specifically, the method involves using γ-butyrolactone and monomethylamine in a molar ratio of 1:1.08 to 1:1.3, and conducting the reaction in a single step at 340-380°C and an absolute pressure of 70-120 bar. The feed mixture contains less than 10% water by weight. This method offers certain advantages when operating at a high equipment manufacturing capacity. For example, the reaction process disclosed in CN103351321A is as follows: GBL fine product is mixed with a monomethylamine solution with a mass concentration of 40% and then enters the alkanone reaction bed, where it fully reacts under high temperature and high pressure conditions to produce crude NMP. The reaction temperature is 265-285°C and the reaction pressure is 6.5-8.0 MPa.

[0010] However, the above-mentioned traditional reaction processes do not consider the energy conservation of the reaction system, that is, how to reduce the energy consumption of the reaction system, especially the heat source consumption, and all require the addition of external heat to maintain the temperature of the reaction system.

[0011] At the same time, the conversion rate of butyrolactone, especially the measurement of residual butyrolactone, is also not a concern of current technologies. This is because butyrolactone and alkyl pyrrolidones, such as methyl pyrrolidone, have almost no difference in boiling point and a relative volatility close to 1, making separation difficult and hindering the improvement of subsequent product quality. Summary of the Invention

[0012] In order to solve the above problems, the present invention provides an energy-saving method for preparing pyrrolidone. The present invention utilizes the condensation process of γ-butyrolactone and organic amine or ammonia as a typical exothermic process, and obtains accurate thermodynamic parameters based on basic research, optimizes and simulates the process, and fully utilizes the reaction exotherm. As a result, the reaction system not only does not require an external heat source, but can also generate heat for external use, and can also save circulating water, thereby significantly reducing the amount of circulating water.

[0013] In order to achieve the above object, the present invention provides the following technical solutions:

[0014] The present invention provides a method for preparing energy-saving pyrrolidone, comprising the following steps:

[0015] 1) Gamma-butyrolactone is mixed with an organic amine or aqueous ammonia, and the mixture is passed through a stage I reactor, a stage II reactor, a stage II reactor or a stage II reactor and a laminar flow reactor to obtain a hot material;

[0016] 2) passing the material obtained in step 1) through the stage I reactor, condenser and constant pressure tank described in step 1 in sequence to obtain pyrrolidone;

[0017] The pressure of the constant pressure tank is 1-8 MPa; preferably 2-5 MPa; most preferably 3.5-4.5 MPa;

[0018] The shell-and-tube reactor is provided with an additional forced heat transfer element;

[0019] The pyrrolidone is 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone or N-octyl-2-pyrrolidone.

[0020] Preferably, the first-stage reactor in step 1) is a shell-and-tube reactor.

[0021] The residence time in the stage I reactor is 1 to 20 minutes, and the outlet temperature of the cold material is 210 to 255°C;

[0022] The I-stage reactor meets the following requirements: the empty tube Reynolds number Re in the I-stage reactor tube is controlled to be ≥6000, and the enhanced Reynolds number Re is ≥9000;

[0023] The inner diameter of the tubes of the stage I reactor is 15-70 mm;

[0024] The tube length of the stage I reactor is 6 to 12 m;

[0025] The structure of the stage I reactor is a horizontal structure;

[0026] The first-stage reactor adopts a multi-tube structure with more than 4 tube passes;

[0027] When the temperature of the material in the stage I reactor is 10-160°C, it enters the condenser, preferably 142-151°C.

[0028] Preferably, the stage II reactor in step 1) is a shell-and-tube reactor, the reaction temperature is 210-265° C., and the residence time in the stage II reactor is 15-40 min;

[0029] The II-stage reactor meets the following requirements: the empty tube Reynolds number Re in the II-stage reactor tube is controlled to be ≥6000, and the enhanced Reynolds number Re is ≥9000;

[0030] The inner diameter of the tubes of the II-stage reactor is 15-70 mm;

[0031] The tube length of the II-stage reactor is 6 to 12 m;

[0032] The structure of the II-stage reactor is a horizontal structure;

[0033] The stage II reactor adopts a multi-tube-pass structure, and the number of tube passes is greater than 4.

[0034] Preferably, the II-level or higher reactor in step 1) is a shell-and-tube reactor, the residence time is 15-40 minutes, and the reaction temperature is 250-285°C;

[0035] The reactor of level II or above meets the following requirements: the empty tube Reynolds number Re in the reactor tube of level II or above is controlled to be ≥2500, and the enhanced Reynolds number Re is ≥6000;

[0036] The inner diameter of the tubes of the reactors above level II is 40-120 mm;

[0037] The tube length of the reactor above level II is 6 to 12 m;

[0038] The structure of the reactor above level II is a horizontal structure;

[0039] The reactors above level II adopt a multi-tube-pass structure, and the number of tube passes is greater than 4.

[0040] Preferably, in step 1), the Reynolds number of the laminar flow reactor is ≤100, and the residence time is 55-60 min.

[0041] Preferably, in step 1), the molar ratio of γ-butyrolactone to the organic amine is 1:1.02-1.4, preferably 1:1.03-1.25, more preferably 1:1.04-1.15, 1:1.1;

[0042] The organic amine is mixed with γ-butyrolactone in the form of an organic amine solution, wherein the mass percentage of the organic amine solution is 30-100%, preferably 40-90%, more preferably 40-80%; 75%.

[0043] Preferably, the organic amine includes methylamine.

[0044] Preferably, in step 1), the molar ratio of γ-butyrolactone to ammonia in aqueous ammonia is 1:1.02-1.4, preferably 1:1.03-1.25, more preferably 1:1.04-1.15, 1:1.3;

[0045] The mass percentage of the ammonia water is 20-90%, preferably 30-80%, more preferably 40-80%; 90%.

[0046] The characteristic technical points of the present invention are:

[0047] 1. The reactor in the preparation method consists of two or more independent reactors;

[0048] 2. After the room temperature γ-butyrolactone and organic amine or ammonia are mixed, they are first subjected to a partition-type heat exchange with the reacted materials. The residence time in the heat exchanger is 1 to 20 minutes. This is the first-stage reactor. Then, they enter the second-stage or higher reaction system with heat transfer medium.

[0049] 3. The amination reactor of level II or above is in the form of a shell-and-tube heat exchanger, wherein the tube side of the amination reactor of level II or above is the reaction medium, and there are strengthening elements in the tube side to increase the mass transfer effect;

[0050] 4. The reaction temperature of the II reactor is controlled at 210~260℃, and that of the III and above reactors is controlled at 250~280℃; the residence time of the II reactor is controlled at 15~40min;

[0051] The spoiler reinforcement inner part described in the present invention can be selected from twisted iron, metal spiral ring, metal wire sheet, metal coil, metal spring, and the suitable range of the spoiler reinforcement inner part is to achieve Re enhancement to the requirements of the present invention.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] 1. No external heating is required to ensure the heat supply for the reaction; the by-product heat can also be used for subsequent distillation processes;

[0054] 2. The reaction pressure is reduced, which reduces the design pressure of the equipment and improves the intrinsic safety;

[0055] 3. The conversion rate is improved and the amount of residual γ-butyrolactone is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below.

[0057] Figure 1 is a reaction process flow chart, wherein 1 γ-butyrolactone feed pump, 2 methylamine feed pump 3, stage I reactor 4, stage II reactor 5, stage III reactor 6, laminar flow reactor 7, condenser 8, constant pressure tank γ-butyrolactone and methylamine or ammonia water are mixed through the pump and enter the stage I reactor, stage II reactor, stage III reactor and laminar flow reactor to obtain the product and the material of the stage I reactor through inter-wall heat exchange, and then the product is condensed through the condenser and finally enters the constant pressure tank. Implementation Method

[0058] The present invention provides a method for preparing energy-saving pyrrolidone, comprising the following steps:

[0059] 1) Gamma-butyrolactone is mixed with an organic amine or aqueous ammonia, and the mixture is passed through a stage I reactor, a stage II reactor, a stage II reactor or a stage II reactor and a laminar flow reactor to obtain a hot material;

[0060] 2) passing the material obtained in step 1) through the stage I reactor, condenser and constant pressure tank described in step 1 in sequence to obtain pyrrolidone;

[0061] The pressure of the constant pressure tank is 1-8 MPa; preferably 2-5 MPa; most preferably 3.5-4.5 MPa;

[0062] The shell-and-tube reactor is provided with an additional forced heat transfer element;

[0063] The pyrrolidone is 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone or N-octyl-2-pyrrolidone.

[0064] The invention mixes gamma-butyrolactone with organic amine or ammonia water, and sequentially passes through a level I reactor, a level II reactor, reactors above level II and a laminar flow reactor to obtain hot materials.

[0065] In the present invention, the first-stage reactor is preferably a shell-and-tube reactor, the residence time in the first-stage reactor is 1 to 20 minutes, and the outlet temperature of the cold material is 210 to 255° C. The first-stage reactor meets the following requirements: the empty tube Reynolds number Re in the first-stage reactor tube is controlled to be ≥6000, and the enhanced Reynolds number Re is ≥9000;

[0066] The inner diameter of the tubes of the stage I reactor is 15-70 mm; the length of the tubes of the stage I reactor is 6-12 m;

[0067] The structure of the stage I reactor is a horizontal structure; the stage I reactor adopts a multi-tube structure with the number of tube passes being greater than 4; when the temperature of the material in the stage I reactor is 10-160°C, it enters the condenser, preferably 142-151°C.

[0068] In the present invention, the II-stage reactor is preferably a shell-and-tube reactor, the reaction temperature is 210-265°C, and the residence time in the II-stage reactor is 15-40 min; the II-stage reactor meets the following requirements: the empty tube Reynolds number Re in the II-stage reactor tube is controlled to be ≥6000, and the enhanced Reynolds number Re is ≥9000; the inner diameter of the shell and tube of the II-stage reactor is 15-70 mm; the shell and tube length of the II-stage reactor is 6-12 m; the structure of the II-stage reactor is a horizontal structure; the II-stage reactor adopts a multi-tube structure, and the number of tube passes is greater than 4.

[0069] In the present invention, the reactor of level II or above is preferably a shell and tube reactor with a residence time of 15 to 40 minutes and a reaction temperature of 250 to 285°C; the reactor of level II or above meets the following requirements: the empty tube Reynolds number Re in the tube of the reactor of level II or above is controlled to be ≥2500, and the enhanced Reynolds number Re is ≥6000; the inner diameter of the shell and tube of the reactor of level II or above is 40 to 120 mm; the shell and tube length of the reactor of level II or above is 6 to 12 m; the structure of the reactor of level II or above is a horizontal structure; the reactor of level II or above adopts a multi-tube structure, and the number of tube passes is greater than 4.

[0070] In the present invention, the Reynolds number (Re) of the laminar flow reactor is ≤100, and the residence time is 55-60 min. In the present invention, the molar ratio of γ-butyrolactone to the organic amine is 1:1.02-1.4, preferably 1:1.03-1.25, more preferably 1:1.04-1.15, or 1:1.1. In the present invention, the organic amine is preferably mixed with γ-butyrolactone in the form of an organic amine solution, wherein the mass percentage of the organic amine solution is 30-100%, preferably 40-90%, more preferably 40-80%; 75%. In the present invention, the organic amine preferably comprises methylamine. In the present invention, the molar ratio of γ-butyrolactone to ammonia in aqueous ammonia is 1:1.02-1.4, preferably 1:1.03-1.25, more preferably 1:1.04-1.15, or 1:1.3. In the present invention, the mass percentage of the ammonia water is 20-90%, preferably 30-80%, more preferably 40-80%; 90%.

[0071] The present invention sequentially passes the obtained material through the I-stage reactor, condenser and constant pressure tank described in step 1 to obtain pyrrolidone; the pressure of the constant pressure tank is 1-8 MPa; preferably 2-5 MPa; most preferably 3.5-4.5 MPa;

[0072] The shell-and-tube reactor is provided with an additional forced heat transfer element; the pyrrolidone is 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone or N-octyl-2-pyrrolidone.

[0073] The present invention calculated through the UNIFAC model and found that in the amination process, taking the synthesis of N-methylpyrrolidone as an example:

[0074]

[0075] Reaction steps (1) and (2) are both exothermic reactions, wherein the reaction heat of reaction step (1) is -42.9 KJ / mol, and the reaction heat of reaction step (2) is -43.8 KJ / mol. This theoretical research finding is the foundation of the present invention.

[0076] The synthesis steps of other organic amines and butyrolactone are the same as above.

[0077] In the present invention, the pyrrolidone is preferably N-methylpyrrolidone or 2-pyrrolidone.

[0078] In order to further illustrate the present invention, the present invention is described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention. Example

[0079] In the reaction unit of a 35,000 ton / year N-methylpyrrolidone device, 4.45 ton / hour of γ-butyrolactone and 2.35 ton / hour of a 75 wt% aqueous methylamine solution (the molar ratio of γ-butyrolactone to methylamine is 1:1.1) are first mixed in a mixer and then enter a stage I reactor. The residence time in the stage I reactor is 8.5 min. The outlet temperature of the stage I reactor is 247°C, the internal tube size of the stage I reactor is 45 mm, the reactor tube length is 9 m, the number of tube passes is 10, the calculated empty tube Reynolds number is 15,000, and a tethered spoiler is inserted inside. The enhanced Reynolds number is 24,800. Then, the reactor enters a stage II reactor. The stage II reactor has a tube size of 67 mm, a reactor length of 9 m, a number of tube passes is 8, a residence time of 20 min, a calculated empty tube Reynolds number is 6,900, a tethered spoiler is inserted inside, and the enhanced Reynolds number is 14,800. The reaction temperature is controlled at 255-258°C by adding fresh heat transfer oil at 248-250°C. The reactor tube size of the stage III reactor is 89mm, the reactor length is 9m, the number of tube passes is 4, the residence time is 40min, the calculated empty tube Reynolds number is 2700, and a ribbon-type turbulator is inserted inside. The enhanced Reynolds number is 7200. The reaction temperature is controlled at 257-260°C by controlling the fresh heat transfer oil flow at 248-250°C. Then the material enters the multi-stage laminar flow reactor. The residence time of the multi-stage laminar flow reactor is 60min, the Re number is controlled to 80, and the laminar flow reactor is kept warm. The material at the outlet of the laminar flow reactor is sent to the stage I reactor for heat exchange with the mixed raw materials and cooled to 142°C. It then enters the circulating water condenser. After cooling at 40°C, the material enters the constant pressure tank. The pressure of the constant pressure tank is 4.8MPaG, which is the reaction system pressure. The residual γ-butyrolactone content at the outlet of the constant pressure tank is 12-15 ppm, and the selectivity of N-methylpyrrolidone based on γ-butyrolactone is about 99.7 mol%.

[0080] The temperature of fresh heat transfer oil in stages II and III rises from 248-250°C at the inlet to 257-259°C. It is then sent to the distillation section for heat recovery and then recycled back to the reaction unit. This results in a temperature difference of 4°C and a by-product heat output of 340kW. This means the entire reaction system can provide 340kW of heat without requiring external heat. Example

[0081] In the reaction unit of a 10,000 ton / year 2-pyrrolidone device, 1.36 tons / hour of γ-butyrolactone and 0.39 tons / hour of 90wt% ammonia solution (the molar ratio of γ-butyrolactone to ammonia is 1:1.3) are first mixed in a mixer and then enter the I-stage reactor. The residence time in the I-stage reactor is 10 minutes. The outlet temperature of the I-stage reactor is 248°C, the internal tube size of the I-stage reactor is 38mm, the reactor tube length is 12m, the number of tube passes is 6, the calculated empty tube Reynolds number is 11000, the internal insertion of a tie-type turbulator, and the enhanced Reynolds number is 16800. Then it enters the II-stage reactor. The tube size of the II-stage reactor is 45mm, the reactor length is 12m, the number of tube passes is 6, the residence time is 21min, the calculated empty tube Reynolds number is 7100, the internal insertion of a tie-type turbulator, and the enhanced Reynolds number is 11200. By controlling the supplementation of 2 The reaction temperature is controlled at 265-268°C by controlling the flow rate of fresh heat transfer oil at 58-260°C. The reactor tube size of the stage III reactor is 95mm, the reactor length is 12m, the number of tube passes is 2, the residence time is 28min, the calculated empty tube Reynolds number is 3100, and a ribbon-type turbulent is inserted inside. The enhanced Reynolds number is 5200. The reaction temperature is controlled at 267-270°C by controlling the flow rate of fresh heat transfer oil at 258-260°C. Subsequently, the material enters the multi-stage laminar flow reactor. The residence time of the laminar flow reactor is 55min, the Re number is controlled to be 60, and the laminar flow reactor is kept warm. The material at the outlet of the laminar flow reactor is sent to the stage I reactor for heat exchange with the mixed raw materials and cooled to 151°C. It then enters the circulating water condenser. The material after cooling at 40°C enters the constant pressure tank. The pressure of the constant pressure tank is 2.9MPaG, which is the pressure of the reaction system. The residual γ-butyrolactone content at the outlet of the constant pressure tank was 26-30 ppm, and the selectivity of 2-pyrrolidone based on γ-butyrolactone was approximately 95.3 mol%.

[0082] The temperature of fresh heat transfer oil in stage II and stage III is increased from 258~260℃ at the inlet to 261~263℃, and then sent to the distillation part to recover heat and then continue to circulate back to the reaction unit for use. The temperature difference is 3℃, and the by-product heat is 96kw.

[0083]

[0084] Referring to the method described in CN1043758C for producing N-methylpyrrolidone in a double-tube reactor with a designed capacity of 10,000 tons / year, according to Example 1, 1.1 tons / hour of γ-butyrolactone and 1.2 tons / hour of a 40 wt% aqueous methylamine solution (γ-butyrolactone:methylamine molar ratio of 1:1.2) were directly introduced into a double-tube reactor with an inner diameter of 89 mm. The residence time was 120 minutes. The flow rate of the thermal oil was adjusted to achieve a reaction temperature of 280°C, a supplementary thermal oil temperature of 283-285°C, and a reaction pressure of 6.0 MPa. The material exiting the reactor was directly cooled in a heat exchanger and then transferred to a constant pressure tank. The crude product was finally produced from the constant pressure tank. The residual γ-butyrolactone content at the constant pressure tank outlet was 195-210 ppm, and the selectivity for N-methylpyrrolidone based on γ-butyrolactone was approximately 99.1 mol%. The inlet temperature of fresh heat transfer oil is 283~285℃, the return oil temperature is 280~282℃, and the temperature difference is about 3℃. The heat transfer oil needs to be heated to maintain the system temperature. The heating power is 92kw.

[0085]

[0086] With front and rear heat exchange, without internal parts, reaction conditions and energy consumption

[0087] Taking Example 1 as an example, without internals installed in the reactor tubes and with consistent feed rates, the outlet temperature of the Stage I reactor was 201°C. The temperature control for the Stage II and Stage III reactors, and their subsequent laminar flow reactors, was consistent with Example 1. However, the inlet temperature of the fresh heat transfer oil in Stages II and III was adjusted to 251-253°C. After passing through the reaction system and heating to 252-255°C, it was sent to the distillation section for heat recovery and then recycled back to the reaction unit. This resulted in a 2°C temperature difference and 180 kW of by-product heat. This significantly reduced by-product heat. Furthermore, the residual γ-butyrolactone content at the constant pressure tank outlet was 280-310 ppm, and the selectivity for N-methylpyrrolidone based on γ-butyrolactone was approximately 99.1 mol%, indicating a significant decrease in reaction yield.

[0088]

[0089] There are internal parts and heat exchange, and the time and temperature adjustment of each section exceeds the agreed range

[0090] Taking implementation 2 as an example, internals are installed in the inner tube of the reactor. Under the condition of consistent feed rate, the residence times of the stage I, stage II, stage III reactors and laminar flow reactor are modified to 27 min, 14 min, 14 min and 60 min, respectively. The total residence time remains unchanged. The stage I to stage III reactors are all single-tube reactors; the empty tube Reynolds numbers Re of the stage I to stage III reactors are 2720, 5100 and 5100, respectively, and the enhanced Reynolds numbers Re are 4140, 7080 and 7080, respectively. The outlet reaction temperature of the stage I reactor is 208°C, and the temperature of the stage II and stage III reactors and their subsequent laminar flow reactors is controlled to a reaction temperature of 258~263°C. The reaction temperature of each reactor fluctuates significantly. Fresh heat transfer oil at 258~260°C is used, which is heated to 259~262°C after passing through the reaction system, sent to the distillation part to recover heat, and then continued to circulate back to the reaction unit for use. The temperature difference is 2°C, and the by-product heat is 69 kW. This indicates that the by-product heat is greatly reduced. At the same time, the residual γ-butyrolactone content at the outlet of the constant pressure tank is 90~110ppm, the selectivity of 2-pyrrolidone based on γ-butyrolactone is ~93.7mol%, and the reaction yield is significantly reduced.

[0091]

[0092] As can be seen from the above table, under the same production capacity, the present invention can achieve better yield and raw material conversion rate under lower pressure conditions than the existing technology, compared with the existing technology, thereby reducing equipment investment.

[0093] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing energy-saving pyrrolidone, characterized in that: The following steps are involved: 1) Mixing γ-butyrolactone with an organic amine or aqueous ammonia, and sequentially passing through a Class I reactor, a Class II reactor, a Class II reactor or above, and a laminar flow reactor to obtain a hot material; 2) the material obtained in step 1) is sequentially passed through the first-stage reactor, condenser and constant pressure tank described in step 1 to obtain pyrrolidone; The pressure of the constant pressure tank is 1-8 MPa; preferably 2-5 MPa; most preferably 3.5-4.5 MPa; The shell-and-tube reactor is provided with an additional forced heat transfer element; The pyrrolidone is 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone or N-octyl-2-pyrrolidone.

2. The preparation method according to claim 1, characterized in that: Step 1) The first-stage reactor is a shell-and-tube reactor, The residence time in the stage I reactor is 1-20 min, and the outlet temperature of the cold material is 210-255°C; The I-stage reactor meets the following requirements: the empty tube Reynolds number Re in the I-stage reactor tube is controlled to be ≥6000, and the enhanced Reynolds number Re is ≥9000; The inner diameter of the tubes of the stage I reactor is 15-70 mm; The tube length of the first-stage reactor is 6 to 12 m; The structure of the stage I reactor is a horizontal structure; The first-stage reactor adopts a multi-tube structure, and the number of tubes is greater than 4; The material enters the condenser when the temperature in the stage I reactor is 10-160°C, preferably 142-151°C.

3. The preparation method according to claim 1, characterized in that: Step 1) The II-stage reactor is a shell-and-tube reactor, the reaction temperature is 210-265°C, and the residence time in the II-stage reactor is 15-40 minutes; The II-stage reactor meets the following requirements: the empty tube Reynolds number Re in the II-stage reactor tube is controlled to be ≥6000, and the enhanced Reynolds number Re is ≥9000; The inner diameter of the tubes of the II-stage reactor is 15-70 mm; The tube length of the II-stage reactor is 6 to 12 m; The structure of the II-stage reactor is a horizontal structure; The stage II reactor adopts a multi-tube-pass structure, and the number of tube passes is greater than 4.

4. The preparation method according to claim 1, characterized in that: In step 1), the reactor of level II or above is a shell-and-tube reactor, the residence time is 15-40 minutes, and the reaction temperature is 250-285°C; The reactor of level II or above meets the following requirements: the empty tube Reynolds number Re in the reactor tube of level II or above is controlled to be ≥2500, and the enhanced Reynolds number Re is ≥6000; The inner diameter of the tubes of the reactors above level II is 40-120 mm; The tube length of the reactor above level II is 6 to 12 m; The structure of the reactor above level II is a horizontal structure; The reactors above level II adopt a multi-tube-pass structure, and the number of tube passes is greater than 4.

5. The preparation method according to claim 1, characterized in that: In the step 1), the Reynolds number of the laminar flow reactor is Re≤100, and the residence time is 55-60 min.

6. The preparation method according to claim 1, characterized in that: In the step 1), the molar ratio of γ-butyrolactone to the organic amine is 1:1.02-1.4, preferably 1:1.03-1.25, more preferably 1:1.04-1.15, 1:1.1; The organic amine is mixed with γ-butyrolactone in the form of an organic amine solution, wherein the mass percentage of the organic amine solution is 30-100%, preferably 40-90%, more preferably 40-80%; 75%.

7. The preparation method according to claim 1 or 6, characterized in that: The organic amine includes methylamine.

8. The preparation method according to claim 1, characterized in that: In the step 1), the molar ratio of γ-butyrolactone to ammonia in aqueous ammonia is 1:1.02-1.4, preferably 1:1.03-1.25, more preferably 1:1.04-1.15, 1:1.3; The mass percentage of the ammonia water is 20-90%, preferably 30-80%, more preferably 40-80%; 90%.

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