Apparatus for the production of 2-pyrrolidone

Abstract

The utility model belongs to the field of chemical industry device, concretely relates to a device for preparing 2-pyrrolidone. The device successively includes the ammonolysis reaction tower for carrying out ammonolysis reaction, the deaminase tower for removing ammonia in the reaction system, the dehydration reactor for carrying out dehydration condensation reaction, the light component tower for removing light component impurity, the product tower for removing heavy component impurity and the evaporator for recovering 2-pyrrolidone in heavy component impurity, one or more gas inlets for ammonia nitrogen mixed gas entering ammonolysis reaction tower are arranged on the outer wall of the ammonolysis reaction tower. The device is used to prepare 2-pyrrolidone, and the ammonolysis reaction of gamma-butyrolactone and ammonia can be carried out under mild conditions. The ammonolysis reaction tower is provided with the gas inlet of ammonia nitrogen mixed gas, and the low-temperature ammonia nitrogen mixed gas circulating in gas phase absorbs reaction heat quickly through trace ammonia vaporization, so that the reaction can be carried out under low temperature all the time.

Description

Technical Field

[0001] This utility model belongs to the field of chemical equipment, and specifically relates to an apparatus for preparing 2-pyrrolidone. Background Technology

[0002] 2-Pyrrolidone (2-PY) is a five-membered nitrogen-containing heterocyclic compound found in both natural and non-natural products. It possesses significant pharmaceutical and industrial application value, serving as a key intermediate and fine chemical in pharmaceuticals and organic chemistry. Its non-corrosive and chemically stable properties have garnered widespread attention in pharmaceutical chemistry and fine chemicals. Furthermore, with the development of the biodegradable plastics industry, polypyrrolidone (also known as Nylon 4), a traditional polymer material synthesized from 2-PY monomers, has regained attention due to its excellent biodegradability, becoming a promising material with broad market prospects. However, whether used in pharmaceuticals, fine chemicals, or as a monomer in the synthesis of Nylon-4, 2-PY requires high product quality. Impurities such as γ-butyrolactone (GBL), amides, and heavy components can interfere with downstream polymerization processes, significantly impacting the performance of the final product. Therefore, the quality requirements for 2-PY in this field are becoming increasingly stringent.

[0003] 2-PY has a long history of use, with its synthesis process dating back to the 1930s, discovered by German chemist J. Walter Reppe during his research on acetylene chemicals. Due to the inexpensive and readily available raw materials, the ammonolysis reaction using GBL as a raw material to prepare 2-PY remains the main method for industrial production, and this method has been the most thoroughly studied. However, this method has consistently suffered from common drawbacks such as high energy consumption, low yield, large amounts of residue, and low product quality.

[0004] In organic synthesis reactions involving the ammonolysis of lactone reactants to generate heterocyclic compounds, high temperature and high pressure are recognized as essential conditions. Achieving a more temperate, energy-efficient, and environmentally friendly synthetic process is one of the most promising synthetic strategies. Therefore, there is an urgent need in the art to provide an apparatus for the preparation of 2-PY that is compatible with this temperate, energy-efficient, and environmentally friendly synthetic process. Utility Model Content

[0005] The purpose of this invention is to provide an apparatus for preparing 2-PY.

[0006] The first aspect of this invention provides an apparatus for preparing 2-pyrrolidone, the apparatus comprising, in sequence, an ammonolysis reaction tower for carrying out an ammonolysis reaction, an ammonia removal tower for removing ammonia from the reaction system, a dehydration reactor for carrying out a dehydration condensation reaction, a light component tower for removing light component impurities, a product tower for removing heavy component impurities, and an evaporator for recovering 2-pyrrolidone from the heavy component impurities; one or more inlets for ammonia-nitrogen mixed gas to enter the ammonolysis reaction tower are provided on the outer wall of the ammonolysis reaction tower.

[0007] This utility model has the following beneficial effects: Using the apparatus described herein, the ammonolysis reaction of GBL with ammonia can be carried out under mild conditions to prepare 2-PY. The ammonolysis reaction tower is equipped with an inlet for an ammonia-nitrogen mixture. The low-temperature ammonia-nitrogen mixture circulating in the gas phase rapidly absorbs the heat of reaction through the vaporization of a small amount of ammonia, ensuring that the reaction always proceeds at a low temperature. Using the apparatus described herein, the conversion rate of GBL to prepare 2-PY can be controlled to ≥98%, and the selectivity for the formation of 4-hydroxybutyramide (4-HBA) is high, avoiding the occurrence of side reactions.

[0008] In this device, a temperature control point is set at the feed inlet of the dehydration reactor to ensure that 4-HBA can be heated to above 200°C through rapid heating when the device is used for actual production. This avoids the condensation reaction between GBL and 4-HBA during the heating process below 200°C, thereby reducing the generation of heavy component impurity 4-(N-pyrrolidone)butyramide (PBA). Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the structure of a device in one or more embodiments of this paper.

[0010] The annotations in the attached figures are explained as follows: 1-Ammonium hydrolysis reaction tower; 10-Feed mixer; 11-Feed pump; 12-Feed preheater; 13-Ammonia-nitrogen circulating gas cooler; 14-Ammonia-nitrogen circulating gas blower; 15-Ammonia hydrolysis tower top condenser; 16-Ammonia hydrolysis tower bottom pump; 2-Deammoniation tower; 20-Ammonia water collection tank; 21-Ammonia water return pump; 22-Deammoniation tower reflux pump; 23-Deammoniation tower top condenser; 24-Deammoniation tower low-pressure steam inlet; 25-Deammoniation tower bottom pump; 3-Dehydration reactor; 30-Heater; 31-Heat exchanger; 4-Light component tower; 40-Light component tower Top condenser; 41-Light component column reflux tank; 42-Light component column reflux pump; 43-Light component column vacuum pump; 44-Light component column bottom pump; 45-Light component column reboiler; 5-Product column; 50-Product column reflux tank; 51-Product column reflux pump; 52-Product column top condenser; 53-Product column vacuum pump; 54-Product pump; 55-Product cooler; 56-Product column bottom pump; 57-Product column reboiler; 6-Evaporator; 60-Evaporator condenser; 61-Recovered product collection tank; 62-Recovered product pump; 63-Residue pump. Detailed Implementation

[0011] To enable those skilled in the art to understand the features and effects of this utility model, the terms and expressions mentioned herein are explained and defined in general terms below. Unless otherwise specified, all technical and scientific terms used herein have the common meaning understood by those skilled in the art regarding this utility model, and in case of conflict, the definitions in this specification shall prevail.

[0012] The theories or mechanisms described and disclosed herein, whether right or wrong, should not limit the scope of this invention in any way; that is, the content of this invention can be implemented without being limited by any specific theory or mechanism.

[0013] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0014] In this document, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0015] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0016] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the present invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the present invention.

[0017] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0018] In this article, since the reaction takes place in the liquid phase, "ammonia" refers to any NH3-related chemical substances that may be present in the reaction system other than ammonia gas, such as liquid ammonia, NH3 complexes (e.g., ammonia monohydrate, i.e., NH3·H2O), and ammonium salts (…). All of the above-mentioned ammonia-related compounds are stoichiometric in the form of NH3.

[0019] In this article, "residue" refers to the sum of all unidentified heavy component impurities with high boiling points (≥280℃ at normal pressure) that cannot be identified in the chromatogram during gas chromatography analysis of the product. Residue is generated during the reaction process and may undergo further reactions under high-temperature conditions during distillation or recovery, remaining in the product. High residue content indicates numerous side reactions, resulting in low product yield and purity.

[0020] The method described in this paper includes the following steps in the reaction process for preparing 2-PY: (a) GBL (γ-butyrolactone) and ammonia undergo ring-opening to form 4-hydroxybutyramide (4-HBA): ; Side reactions: ; (b) 4-HBA dehydrates to produce 2-PY: .

[0021] Laboratory tests showed that, due to differences in process condition control, impurities such as 4-(N-pyrrolidone)butyramide (PBA) and 4-hydroxybutyric acid, which are byproducts of step (a), are the main reasons for the low yield and poor product quality of the 2-PY production process.

[0022] The inventors also discovered that the difficulty in preparing 2-PY lies in the volatile and difficult-to-condense properties of liquid ammonia and high-concentration ammonia, which are contrary to the direction of reaction kinetics. Maintaining the liquid-phase reaction system requires high-pressure and high-temperature reaction conditions, which inevitably increase the occurrence of side reactions. Changes in pressure and temperature have a significant impact on the selectivity of intermediate products such as 4-HBA, PBA, and 4-hydroxybutyric acid, potentially leading to an increase in various byproducts such as heavy component impurities (e.g., oligomers of 2-PY), which will significantly reduce the reaction yield and make distillation separation difficult. This is also the main reason for the low reaction yield and poor product quality in current industrial applications. In summary, the inventors found that existing preparation methods mainly have the following problems: In step (a) above, to ensure a high conversion rate of GBL and improve the selectivity of 4-HBA, liquid ammonia or ammonia solution with a high concentration is required, which necessitates a lower temperature to maintain the liquid phase system. However, if the temperature is too low, the reaction rate will decrease significantly, making it uneconomical. Increasing the temperature requires reducing the ammonia concentration, resulting in incomplete GBL conversion. Excessively high temperatures can also lead to ammonia vaporization, increasing the side reactions of GBL hydrolysis and reducing the selectivity of 4-HBA.

[0023] In step (b) above, the dehydration cyclization reaction of 4-HBA requires a high temperature and a suitable reaction concentration. When the temperature is below 200℃, the dehydration cyclization reaction of 4-HBA does not proceed; during the heating process, the main side reaction is the formation of PBA. High-temperature reaction conditions typically lead to an increase in side reactions, and PBA can further transform into other impurities, resulting in an increase in heavy component impurities. Excessively high temperatures also cause ammonia vaporization, affecting the reaction and conversion rate. Furthermore, excessively high temperatures can reverse the reaction, actually reducing the conversion rate.

[0024] Based on this, the inventors provide a method for preparing 2-pyrrolidone. This method uses an ammonia-nitrogen mixture for heat removal and controls the heating time of the reaction solution to 200-300°C, ensuring that the ammonolysis reaction is carried out under relatively mild low-temperature conditions. This results in a high conversion rate of γ-butyrolactone and a high selectivity of 4-hydroxybutyramide after step (a) of the reaction, and a high conversion rate of 4-hydroxybutyramide and a high yield of 2-pyrrolidone after step (b) of the reaction, with a low content of heavy component impurities in the system. Accordingly, this paper also provides an apparatus for carrying out the method for preparing 2-PY described herein.

[0025] This article provides an apparatus for preparing 2-PY, the apparatus comprising, in sequence, an ammonolysis reaction tower for carrying out an ammonolysis reaction, an ammonia removal tower for removing ammonia from the reaction system, a dehydration reactor for carrying out a dehydration condensation reaction, a light component tower for removing light component impurities, a product tower for removing heavy component impurities, and an evaporator for recovering 2-PY from the heavy component impurities; the outer wall of the ammonolysis reaction tower is provided with one or more inlets for the ammonia-nitrogen mixture to enter the ammonolysis reaction tower.

[0026] In some implementations, a temperature control point is provided at the feed inlet of the dehydration reactor to detect the temperature of the material at the feed inlet of the dehydration reactor.

[0027] In some embodiments, the apparatus includes a device inlet for ammonia and GBL to enter the apparatus herein.

[0028] In some embodiments, the device inlet is connected to the inlet of the ammonium hydrolysis tower via a feed mixer and a feed preheater. Preferably, a feed pump is also provided on the pipeline connecting the device inlet and the ammonium hydrolysis tower; more preferably, the feed pump is located on the pipeline connecting the feed mixer and the feed preheater.

[0029] In some embodiments, the inlets for the ammonia-nitrogen mixture to enter the ammonium hydrolysis reaction tower are equidistantly arranged in the extending direction of the ammonium hydrolysis reaction tower.

[0030] In some embodiments, the ammonium hydrolysis reaction tower is provided with multiple trays (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30). The inlet for the ammonia-nitrogen mixture to enter the ammonium hydrolysis reaction tower is located in the middle of two adjacent trays, and an inlet for the ammonia-nitrogen mixture to enter the ammonium hydrolysis reaction tower is optionally located below the bottom tray. Preferably, only one inlet for the ammonia-nitrogen mixture is located in the middle of two adjacent trays, and one inlet for the ammonia-nitrogen mixture is located below the bottom tray.

[0031] In some embodiments, the top of the ammonium hydrolysis reaction tower is provided with a top exhaust port for discharging the ammonia-nitrogen mixture from the ammonium hydrolysis reaction tower; and / or, the bottom of the ammonium hydrolysis reaction tower is provided with a bottom outlet for discharging the reaction liquid from the ammonium hydrolysis reaction tower.

[0032] In some implementations, the exhaust port at the top of the ammonolysis reaction tower is connected to the inlet of the ammonia collection tank via the top condenser of the ammonolysis tower.

[0033] In some embodiments, the ammonia collection tank has a top outlet, which is connected to the inlet of the ammonia-nitrogen mixture on the ammonolysis reaction tower via an ammonia-nitrogen circulating gas fan and an ammonia-nitrogen circulating gas cooler. Preferably, the pipeline connecting the ammonia collection tank and the inlet of the ammonia-nitrogen mixture is also provided with a nitrogen inlet for fresh nitrogen to enter the apparatus. Preferably, the nitrogen inlet is located on the pipeline connecting the ammonia collection tank and the inlet of the ammonia-nitrogen mixture. Preferably, the top outlet of the ammonia collection tank is also connected to a pipeline for discharging the ammonia and nitrogen mixture from the apparatus.

[0034] In some implementations, the bottom outlet of the ammonia collection tank is connected to the inlet of the device. Preferably, an ammonia return pump is also provided on the pipeline connecting the ammonia collection tank and the inlet of the device.

[0035] In some implementations, the bottom outlet of the ammonolysis reaction tower is connected to the inlet of the deammoniation tower. Preferably, an ammonolysis tower bottom pump is installed on the pipeline connecting the ammonolysis reaction tower and the deammoniation tower.

[0036] In some embodiments, the top of the deammoniation tower is provided with a top outlet and a top inlet; and / or, the bottom of the deammoniation tower is provided with a low-pressure steam inlet and a bottom outlet for introducing low-pressure steam into the deammoniation tower. In some embodiments, the bottom outlet of the deammoniation tower is connected to a dehydration reactor.

[0037] In some embodiments, the top outlet of the ammonia removal tower is connected to the inlet of the top condenser of the ammonia removal tower, and the first outlet of the top condenser of the ammonia removal tower is connected to the top inlet of the ammonia removal tower. Preferably, a reflux pump for the ammonia removal tower is installed on the pipeline connecting the top inlet of the ammonia removal tower and the first outlet of the top condenser of the ammonia removal tower. Preferably, the top condenser of the ammonia removal tower is also provided with a second outlet for discharging ammonia water from the apparatus described herein.

[0038] In some implementations, a heater is installed on the pipeline connecting the deammoniation tower and the dehydration reactor; preferably, a heat exchanger is installed on the pipeline connecting the deammoniation tower and the heater; preferably, the bottom outlet of the deammoniation tower is connected to the first inlet of the heat exchanger, and the first outlet of the heat exchanger is connected to the inlet of the heater; preferably, a deammoniation tower bottom pump is also installed on the pipeline connecting the deammoniation tower and the dehydration reactor, preferably, the deammoniation tower bottom pump is installed on the pipeline connecting the deammoniation tower and the heat exchanger.

[0039] The dehydration reactor is provided with a feed inlet at the top; and / or, the dehydration reactor is provided with a discharge outlet at the bottom. In some embodiments, the dehydration reactor is connected to a light component tower via the discharge outlet. Preferably, the discharge outlet of the dehydration reactor is connected to a second feed inlet of the heat exchanger, and the second discharge outlet of the heat exchanger is connected to the light component tower.

[0040] In some implementations, the light component tower is provided with a top outlet and a top inlet at the top, and the bottom of the light component tower is provided with a bottom outlet and a bottom inlet. The area between the top inlet and the bottom inlet is provided with a first inlet connected to the dehydration reactor and a second inlet for feeding the recovered product; preferably, the first inlet is located above the second inlet.

[0041] In some implementations, the top outlet of the light component column is connected to the light component column reflux tank via the light component column top condenser.

[0042] The light component column reflux tank is provided with a top inlet connected to the top outlet of the light component column, a top outlet for discharging non-condensable gases, and a bottom outlet for discharging liquid materials from the light component column reflux tank. The bottom outlet of the light component column reflux tank is connected to the top inlet of the light component column. Preferably, the top outlet of the light component column reflux tank is connected to a pipeline for discharging non-condensable gases from the apparatus. Preferably, a light component column vacuum pump is installed on the pipeline for discharging non-condensable gases from the apparatus. Preferably, a light component column reflux pump is installed on the pipeline connecting the top inlet of the light component column and the bottom outlet of the light component column reflux tank. In some embodiments, a pipeline for discharging light component impurities from the apparatus is also provided on the pipeline connecting the top inlet of the light component column and the bottom outlet of the light component column reflux tank; preferably, the pipeline for discharging light component impurities from the apparatus is located on the pipeline connecting the top inlet of the light component column and the light component column reflux pump.

[0043] In some implementations, the bottom outlet of the light component column is connected to the inlet of the light component column reboiler, and the outlet of the light component column reboiler is connected to the bottom outlet of the light component column.

[0044] In some implementations, the bottom outlet of the light component tower is connected to the product tower; preferably, a light component tower bottom pump is installed on the pipeline connecting the light component tower and the product tower.

[0045] In some implementations, the top of the product tower is provided with a top discharge port and a top feed port, and the bottom of the product tower is provided with a bottom discharge port and a bottom feed port. The area between the top feed port and the bottom feed port is provided with a product discharge port for discharging high-purity 2-PY product from the present device and a feed port connected to the bottom discharge port of the light component tower.

[0046] In some embodiments, the product tower contains one or more sections of packing, such as two, three, four, five, six, seven, eight, nine, or ten sections. The product outlet of the product tower is located in the upper middle part of the product tower, for example, near the top inlet of the product tower. In some embodiments, the location of the product outlet of the product tower is determined based on a calculated number of theoretical trays. Preferably, the product outlet of the product tower is located at the calculated position corresponding to the 2nd to 5th theoretical tray counting downwards from the top of the tower. In some embodiments, the product tower contains four sections of packing, and the product outlet is located between the first and second sections of packing counting downwards from the top of the tower. In some embodiments, the product tower contains five sections of packing, and the product outlet is located between the second and third sections of packing counting downwards from the top of the tower.

[0047] In some implementations, the product outlet of the product tower is connected to a product cooler; preferably, a product pump is installed on the pipeline connecting the product cooler and the product tower.

[0048] In some implementations, the top outlet of the product tower is connected to the product tower reflux tank via the top condenser of the product tower.

[0049] The product tower reflux tank is provided with a top inlet connected to the top outlet of the product tower, a top outlet for discharging non-condensable gases, and a bottom outlet for discharging liquid material from the product tower reflux tank. The bottom outlet of the product tower reflux tank is connected to the top inlet of the product tower. Preferably, the top outlet of the product tower reflux tank is connected to a pipeline for discharging non-condensable gases from the apparatus. Preferably, a product tower vacuum pump is installed on the pipeline for discharging non-condensable gases from the apparatus. Preferably, a product tower reflux pump is installed on the pipeline connecting the top inlet of the product tower and the bottom outlet of the product tower reflux tank.

[0050] In some implementations, the bottom outlet of the product column is connected to the inlet of the product column reboiler, and the outlet of the product column reboiler is connected to the bottom inlet of the product column. Preferably, a product column bottom pump is installed on the pipeline connecting the bottom outlet of the product column and the inlet of the product column reboiler.

[0051] In some implementations, the bottom outlet of the product tower is connected to the evaporator; preferably, a product tower bottom pump is installed on the pipeline connecting the product tower and the evaporator.

[0052] In some embodiments, the evaporator is provided with a bottom outlet for discharging residue from the apparatus, a top inlet connected to the bottom outlet of the product column, and a top outlet for returning the recovered 2-PY product to the light component column. Preferably, a residue pump is provided on the pipeline connected to the bottom outlet of the evaporator for discharging residue from the apparatus.

[0053] In some embodiments, the top outlet of the evaporator is connected to a recycled product collection tank via an evaporator condenser, and the outlet of the recycled product collection tank is connected to the second inlet of the light component tower. Preferably, a recycled product pump is installed on the pipeline connecting the recycled product collection tank and the light component tower.

[0054] In some embodiments, the structure of the device described herein is as follows: Figure 1 As shown. The apparatus described herein includes an ammonolysis reaction tower 1 for carrying out step (a) ammonolysis and a dehydration reactor 3 for carrying out step (b) dehydration condensation. Preferably, a deammoniation tower 2 for removing ammonia from the reaction system during the ammonolysis reaction is also provided between the ammonolysis reaction tower 1 and the dehydration reactor 3. Further, the apparatus also includes a light component tower 4 and a product tower 5 located downstream of the dehydration reactor 3, that is, the apparatus described herein includes an ammonolysis reaction tower 1, a deammoniation tower 2, a dehydration reactor 3, a light component tower 4, and a product tower 5 arranged sequentially. Preferably, the apparatus also includes an evaporator 6 for recovering 2-PY from the heavy components discharged from the bottom of the product tower 5 to improve the yield.

[0055] In this paper, the reboilers installed at the bottom of each column are used to provide a heat source for the column, thereby evaporating the material in the bottom of the column. In this apparatus, the bottom of the light component column is connected to a light component column reboiler for providing a heat source for the light component column; the bottom of the product column is connected to a product column reboiler for providing a heat source for the product column.

[0056] In this paper, the ammonia hydrolysis reaction tower 1 includes a feed inlet for ammonia water and GBL feed, a mixer inlet for ammonia nitrogen mixed gas to enter the ammonia hydrolysis reaction tower 1, a tower top exhaust port for discharging the ammonia nitrogen mixed gas in the reaction system, and a tower bottom outlet for discharging the reaction liquid.

[0057] In some embodiments, the apparatus further includes a feed inlet for ammonia and GBL to enter the apparatus, which is connected to the feed inlet of the ammonolysis reaction tower 1 via a feed mixer 10. In actual production, after ammonia and GBL enter the apparatus through the feed inlet, they are first premixed in the feed mixer 10 before entering the ammonolysis reaction tower 1 for the ammonolysis reaction. Preferably, a feed pump 11 is also installed on the pipeline connecting the feed mixer 10 and the ammonolysis reaction tower 1.

[0058] In some embodiments, the feed inlets for ammonia and GBL entering the unit are connected in sequence to the feed inlet of the ammonolysis reaction tower 1 via a feed mixer 10, a feed pump 11, and a feed preheater 12.

[0059] The exhaust port at the top of the ammonium hydrolysis reaction tower 1 is connected to the inlet of the ammonia collection tank 20. Preferably, an ammonium hydrolysis tower top condenser 15 is also provided between the exhaust port at the top of the ammonium hydrolysis reaction tower 1 and the inlet of the ammonia collection tank 20. The bottom outlet of the ammonia collection tank 20 is connected to the inlet of the device for ammonia entering the apparatus described herein via an ammonia return pump 21.

[0060] The ammonia collection tank 20 is also equipped with a top outlet at the top, which regulates the pressure inside the ammonolysis reaction tower 1 by discharging nitrogen and ammonia gas. The top outlet is connected to the mixer inlet of the ammonolysis reaction tower 1; alternatively, the top outlet is connected to a pipeline for discharging a portion of the mixed gas including nitrogen and ammonia. Preferably, the top outlet is connected to the mixer inlet of the ammonolysis reaction tower 1 in sequence via an ammonia-nitrogen circulating gas fan 14 and an ammonia-nitrogen circulating gas cooler 13. A nitrogen inlet for fresh nitrogen gas to enter the apparatus is also provided on the pipeline connecting the top outlet to the ammonia-nitrogen circulating gas fan 14.

[0061] In actual production, a portion of the ammonia-nitrogen mixture discharged from the top outlet of the ammonia collection tank 20 is discharged externally, while the remaining portion, after mixing with fresh nitrogen, passes sequentially through the ammonia-nitrogen circulating gas fan 14 and the ammonia-nitrogen circulating gas cooler 13 before entering the ammonia decomposition reaction tower 1. Ammonia water discharged from the bottom outlet of the ammonia collection tank 20 is returned to the unit's feed inlet via the ammonia return pump 21, and then re-enters the ammonia decomposition reaction tower 1 via the feed mixer 10, the feed pump 11, and the feed preheater 12. The ammonia decomposition reaction tower 1 is equipped with 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 trays.

[0062] In some implementations, a mixer inlet is provided on the outer wall of the ammonolysis reaction tower. There may be one or more mixer inlets, such as five. In some implementations, only one mixer inlet is provided between two adjacent trays of the ammonolysis reaction tower, and only one mixer inlet is provided below the bottom tray.

[0063] In some implementations, the bottom outlet of the ammonolysis reaction tower 1 is connected to the inlet of the deammoniation tower 2 via the ammonolysis tower bottom pump 16.

[0064] In this paper, the ammonia stripping tower 2 is used to remove ammonia from the reaction liquid of the ammonolysis reaction. The ammonia stripping tower 2 is a stripping tower to reduce the temperature and residence time of the ammonia stripping process. The top of the ammonia stripping tower 2 is equipped with a top outlet and a top inlet. The bottom of the ammonia stripping tower 2 is equipped with a bottom outlet and a low-pressure steam inlet 24.

[0065] In some embodiments, the top outlet of the ammonia removal tower 2 is connected to the top condenser 23 of the ammonia removal tower. In some embodiments, the second outlet of the top condenser 23 of the ammonia removal tower is connected to a pipeline for discharging ammonia water from the present invention, and / or the first outlet of the top condenser 23 of the ammonia removal tower is connected to the top inlet of the ammonia removal tower 2. Preferably, a reflux pump 22 for the ammonia removal tower is also provided between the first outlet of the top condenser 23 of the ammonia removal tower and the top inlet of the ammonia removal tower 2. In actual production, the gaseous mixture of ammonia and water discharged from the top of the ammonia removal tower 2 enters the top condenser 23 of the ammonia removal tower and is cooled into a liquid state. Since the gaseous mixture of ammonia and water also contains reaction liquid, part of the liquid material cooled by the top condenser 23 of the ammonia removal tower is discharged from the present invention, and part of it is re-entered into the ammonia removal tower 2 by the ammonia tower reflux pump 22.

[0066] In some implementations, the low-pressure steam inlet 24 of the deammoniation tower 2 is connected to a pipeline for introducing low-pressure steam into the deammoniation tower 2.

[0067] In some implementations, the outlet of the deammoniation tower 2 is connected to the inlet of the heater 30 via a pipeline, and the outlet of the heater 30 is connected to the inlet of the dehydration reactor 3 via a pipeline. A deammoniation tower bottom pump 25 and a heat exchanger 31 are also provided between the deammoniation tower 2 and the heater 30. The first inlet of the deammoniation tower 2 is connected to the heat exchanger 31, and the first outlet of the heater 30 is connected to the heat exchanger 31. The deammoniation tower bottom pump 25 is preferably located on the pipeline connecting the deammoniation tower 2 and the heat exchanger 31. In actual production, low-pressure steam (0.13 MPa, 110°C) is introduced into the bottom of the deammoniation tower to prevent the bottom material from circulating at high temperature for extended periods, thereby reducing the occurrence of side reactions. The deammoniation reaction liquid discharged from the bottom of the tower is transported to the dehydration reactor 3 for dehydration condensation reaction. The reaction liquid transported to the dehydration reactor 3 is first preheated by the heat exchanger 31, then heated to the reaction temperature in the heater 30 before entering the dehydration reactor 3.

[0068] The dehydration reactor 3 has a feed inlet at its top that connects to the outlet of the heater 30, and a discharge outlet at its bottom that discharges the reaction liquid. The discharge outlet of the dehydration reactor 3 is connected to the second feed inlet of the heat exchanger 31, which exchanges heat from the reaction liquid discharged from the bottom of the dehydration reactor 3 to the reaction liquid before it enters the heater 30. The second discharge outlet of the heat exchanger 31 is connected to the first feed inlet of the light component tower 4.

[0069] A temperature control point is installed at the feed inlet of the dehydration reactor 3. In this paper, the heating time of the liquid material is calculated from the time the liquid material enters the heater 30 until it enters the dehydration reactor 3. In actual production, the heating time of the liquid material is controlled to be ≤10min (or ≤5min, or ≤2min), and the temperature of the liquid material after being heated by the heater 30 is confirmed to be 200-300℃ through the temperature control point.

[0070] The light component column 4 has a top discharge port and a top feed port at its top, and a bottom discharge port and a bottom feed port at its bottom. The middle section of the light component column 4 has a first feed port connected to the dehydration reactor 3 and a second feed port for product recovery. The middle section of the light component column 4 refers to the area between the top feed port and the bottom feed port. The first feed port is located near the top of the column, and the second feed port is located near the bottom of the column.

[0071] The top outlet of the light component column 4 is connected to the light component column reflux tank 41 via the light component column top condenser 40. The light component column reflux tank 41 is equipped with a top inlet connected to the top outlet of the light component column 4, a top outlet for discharging non-condensable gases, and a bottom outlet for discharging liquid materials from the light component column reflux tank. The top outlet of the light component column reflux tank 41 is connected to a pipeline for discharging non-condensable gases from the apparatus, preferably equipped with a light component column vacuum pump 43. The bottom outlet of the light component column reflux tank 41 is connected to the top inlet of the light component column 4. A light component column reflux pump 42 is installed on the pipeline connecting the bottom outlet of the light component column reflux tank 41 and the top inlet of the light component column 4. A pipeline for discharging some light component impurities from the apparatus is also installed on the pipeline connecting the top inlet of the light component column 4 and the light component column reflux pump 42. In actual production, gaseous light component impurities (including non-condensable gases) carrying the product are discharged from the top of the light component tower. The non-condensable gases and the liquid material obtained by cooling by the light component tower top condenser 40 enter the light component tower reflux tank 41. Part of the liquid material in the light component tower reflux tank 41 is discharged from the apparatus described herein, and part is returned to the light component tower 4 to recover the product. The non-condensable gases are discharged from the apparatus described herein through the light component tower vacuum pump 43.

[0072] The outlet of the bottom of the light component column 4 is connected to the inlet of the reboiler 45, and the outlet of the reboiler 45 is connected to the inlet of the bottom of the light component column 4. In actual production, the discharge from the bottom of the light component column 4 is mainly the reaction liquid of product 2-PY. Part of the material discharged from the bottom of the light component column 4 enters the product column 5 to remove heavy component impurities, and part of it is heated and evaporated in the reboiler 45 before returning to the light component column.

[0073] In some implementations, the bottom outlet of the light component tower 4 is connected to the product tower 5, and a light component tower bottom pump 44 is also installed on the pipeline connecting the light component tower 4 and the product tower 5.

[0074] Product tower 5 has a top discharge port and a top feed port at its top, and a bottom discharge port and a bottom feed port at its bottom. A product discharge port and a feed port connecting to the light component tower 4 are located in the middle of product tower 5. The middle of product tower 5 refers to the position between the top feed port and the bottom feed port. Preferably, the product discharge port and feed port of product tower 5 are located near the top feed port.

[0075] The top outlet of product column 5 is connected to product column reflux tank 50 via product column top condenser 52. Product column reflux tank 50 is equipped with a top inlet connected to the top outlet of product column 5, a top outlet for discharging non-condensable gases, and a bottom outlet for discharging liquid materials within the product column reflux tank. Product column reflux tank 50 is primarily used to hold the 2-PY product carrying a small amount of impurities discharged from the top outlet of product column 5. Compared to the 2-PY discharged from the product outlet of product column 5, the purity of the 2-PY in product column reflux tank 50 is slightly lower. The top outlet of product column reflux tank 50 is connected to a pipeline for discharging non-condensable gases from the apparatus, preferably equipped with a product column vacuum pump 53. The bottom outlet of product column reflux tank 50 is connected to the top inlet of product column 5. A product column reflux pump 51 is installed on the pipeline connecting the bottom outlet of product column reflux tank 50 and the top inlet of product column 5. In actual production, the gaseous mixture discharged from the top of product tower 5 is cooled by the product tower top condenser 52 and then enters the product tower reflux tank 50. The non-condensable gas in it is discharged out of the device by the product tower vacuum pump 53, and the liquid 2-PY product carrying impurities is all returned to product tower 5.

[0076] Product tower 5 is connected to product cooler 55 via product outlet, and product cooler 55 discharges high-purity 2-PY. Product pump 54 is also installed on the pipeline connecting product tower 5 and product cooler 55.

[0077] In some implementations, the product tower 5 is provided with four sections of packing, and the product outlet is located between the first and second sections of packing, counting downwards from the top of the tower.

[0078] The outlet of the product column 5 is connected to the inlet of the product column reboiler 57, and the outlet of the product column reboiler 57 is connected to the inlet of the product column 5. A product column reboiler pump 56 is also installed on the pipeline connecting the outlet of the product column 5 and the inlet of the product column reboiler 57.

[0079] In some implementations, the bottom outlet of product column 5 is connected to evaporator 6 for recovering 2-PY from heavy component impurities. A product column bottom pump 56 is also installed on the pipeline connecting product column 5 and evaporator 6. In actual production, the heavy component impurities discharged from the bottom outlet of product column 5 are partially reheated by product column reboiler 57 and then re-enter product column 5, while the remaining heavy component impurities enter evaporator 6 to recover the 2-PY product mixed in with the heavy component impurities.

[0080] Evaporator 6 is provided with a feed inlet, a product outlet, and a residue outlet. Evaporator 6 is connected to the bottom outlet of product tower 5 via the feed inlet. Preferably, evaporator 6 is a thin-film evaporator. The residue outlet of evaporator 6 is connected to a pipeline for discharging residue from the apparatus, and preferably, a residue pump 63 is also installed on this pipeline. The product outlet of evaporator 6 is connected to a recycled product collection tank 61 via evaporator condenser 60. The outlet of recycled product collection tank 61 is connected to the second feed inlet of light component tower 4. A recycled product pump 62 is also installed on the pipeline connecting light component tower 4 and recycled product collection tank 61.

[0081] method

[0082] This article provides a method for preparing 2-pyrrolidone, the method comprising the following steps: (1) γ-Butyrolactone and ammonia undergo a nucleophilic reaction to obtain a first reaction solution containing 4-hydroxybutyramide; (2) Heat the first reaction solution to 200-300℃ to obtain the second reaction solution; (3) The 4-hydroxybutyramide in the second reaction solution undergoes a dehydration condensation reaction to obtain a third reaction solution containing 2-pyrrolidone; In step (2), the heating time for heating the first reaction solution to 200°C is ≤10 min.

[0083] In step (1), the low-temperature, high-concentration ammonia reaction conditions are beneficial for improving the conversion rate of the raw material GBL and the selectivity of the product 4-HBA. Due to the basicity of ammonia and its strong nucleophilicity, the ammonolysis of GBL lactone can proceed spontaneously without a catalyst. GBL undergoes ammonolysis to produce 4-HBA under the action of liquid ammonia or high-concentration ammonia, which can be carried out at low temperatures of 10-50℃. If the reaction temperature is too high, it will intensify the hydrolysis of GBL to produce 4-hydroxybutyric acid. When 4-HBA is at ≥100℃, the reaction shifts in the reverse direction and decomposes into GBL + NH3. Therefore, step (1) should be strictly controlled under low reaction temperature and high ammonia concentration conditions. By removing the heat of reaction in time, step (1) keeps the reaction under low-temperature conditions, converting GBL to 4-HBA with a high conversion rate.

[0084] In step (1), GBL undergoes ammonolysis with high-concentration ammonia as a raw material. High-concentration ammonia is beneficial for improving the conversion rate of GBL. The high-concentration ammonia can be liquid ammonia or ammonia water with a high concentration. In the ammonia water, the molar concentration of ammonia is 40-100% (when the molar concentration is 100%, it is liquid ammonia). In some embodiments, the ammonia for the nucleophilic reaction in step (1) is derived from concentrated ammonia water or liquid ammonia with a molar concentration ≥40%. The molar concentration of ammonia in the concentrated ammonia water can be 40-70% or 70-90%. Using concentrated ammonia water or liquid ammonia with the concentrations defined herein for the reaction in step (1) can improve the conversion rate of the raw material GBL and the selectivity of the product 4-HBA.

[0085] In step (1), the reaction is carried out under low temperature conditions. The reaction temperature of step (1) is 10-50°C, preferably 20-50°C, more preferably 30-40°C or 25-35°C. Controlling step (1) to be carried out at the temperature defined herein can improve the conversion rate of the feedstock GBL and the selectivity of the product 4-HBA.

[0086] The reaction pressure in step (1) can be 1 bar to 30 bar, for example 1 to 10 bar, 3 to 8 bar or 4 to 6 bar.

[0087] The dwell time in step (1) can be 5-15 minutes, for example, 5-10 minutes or 10-15 minutes.

[0088] In step (1), the molar ratio of γ-butyrolactone to ammonia is 1:(1.05-3), for example 1:(1.1-2), 1:(1.1-1.5), 1:(1.1-1.2).

[0089] In some implementations, step (1) is carried out in the absence of a catalyst.

[0090] In some implementations, in step (1), an ammonia-nitrogen mixture is introduced into the reaction system for heat removal. Specifically, step (1) employs a tower reactor, with GBL and high-concentration ammonia fed from the top of the tower. The ammonia-nitrogen mixture enters the reactor through multiple access points located between the trays of the tower reactor to ensure uniform reaction temperature on each tray. These access points are preferably evenly distributed axially from the top of the tower to the bottom. As the ammonia-nitrogen mixture passes through the trays, it reduces the activation energy, rapidly removes heat, and increases heat and mass transfer during the reaction process, enabling the unidirectional conversion of GBL+NH3 to 4-HBA, thereby avoiding an increase in side reactions.

[0091] In some implementations, the total molar number of ammonia and nitrogen in the ammonia-nitrogen mixture is in a molar ratio of 1:(1-1000) to the feed GBL, for example 1:(1-500), 1:(1-100), 1:(10-100), 1:(50-100), 1:(80-100).

[0092] In some embodiments, the molar concentration of ammonia in the ammonia-nitrogen mixture is 0.1-99%, for example 1%, 10%, 20%, 30%, 50%, 60%, 70%, 80%, 95%, 99%, preferably 50-80%, 80-99%, 80-95%, 75-85%.

[0093] In some embodiments, the inlet temperature of the ammonia-nitrogen mixture can be 10-50°C, for example 10°C, 20°C, 30°C, or 40°C, preferably 20-40°C or 25-35°C, and preferably the same as the reaction temperature inside the reactor.

[0094] In some embodiments, the inlet pressure of the ammonia-nitrogen mixture can be 10-40 bar, for example, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, preferably 10-20 bar, 15-30 bar, 10-15 bar, and more preferably 10 bar higher than the reaction pressure inside the reactor.

[0095] Existing conventional heat removal methods, such as external circulation heat removal and internal cooling heat removal, all result in a certain temperature rise in the reaction system, high energy consumption, and back mixing of the reaction liquid, leading to an increase in the final residue. Compared with other conventional heat removal methods, this paper uses ammonia-nitrogen mixed gas for heat removal. By utilizing the mechanism of ammonia vaporization for heat removal, the temperature uniformity of the reaction system can be maintained to the maximum extent, avoiding the occurrence of more side reactions, thereby improving the purity and yield of the product. In summary, by using ammonia-nitrogen mixed gas for heat removal in step (1), and controlling the amount of ammonia-nitrogen mixed gas relative to GBL, controlling the molar concentration of ammonia in the ammonia-nitrogen mixed gas, and controlling the inlet temperature and inlet pressure of the ammonia-nitrogen mixed gas within the range defined in this paper, the conversion rate of raw material GBL and the selectivity of product 4-HBA can be improved.

[0096] In some embodiments, in step (1), the conversion of the nucleophilic γ-butyrolactone is ≥98%, preferably ≥99%, and more preferably ≥99.4%.

[0097] In some embodiments, in step (1), the selectivity of the nucleophilic 4-hydroxybutyramide is ≥95%, preferably ≥96%, ≥97%, ≥98%, or ≥99%.

[0098] In some embodiments, the content of γ-butyrolactone in the first reaction solution is ≤1.00wt%, preferably ≤0.50wt%.

[0099] In some embodiments, the content of 4-hydroxybutyramide in the first reaction solution is ≥85.00wt%, preferably ≥90.00wt%.

[0100] In some embodiments, the ammonia content in the first reaction solution is ≤1.00wt%, preferably ≤0.90wt%.

[0101] In some embodiments, the residue content in the first reaction solution is ≤2.00wt%, preferably ≤1.00wt%, and more preferably ≤0.70wt%.

[0102] In contrast to step (1), step (3) requires high-temperature, short-residence-time reaction conditions, and the concentration of 4-HBA in the reaction solution cannot be too high. At 150-170°C, 4-HBA will begin to undergo a condensation reaction with GBL to generate PBA, a non-degradable heavy component. The presence of PBA will reduce the yield of 2-PY and affect product quality. When 4-HBA reaches above 200°C, it will undergo a dehydration reaction to generate 2-PY, which is a slightly exothermic reaction. Therefore, during the process of heating from low temperature to above 200°C, the residence time in the 150-170°C range is the main factor affecting the PBA content. To reduce the PBA content and increase the yield of 2-PY, the heating time needs to be shortened to reach above 200°C with the shortest possible residence time. Therefore, in step (2), the heating time of the reaction solution to 200°C can be further controlled to ≤5 min, preferably ≤3 min, ≤2 min, or ≤1 min. By controlling the heating time of the first reaction solution to 200-300℃ in step (2) within the range defined herein, the content of heavy component impurities (especially PBA) in step (3) can be effectively reduced, thereby increasing the yield of 2-pyrrolidone.

[0103] In step (2), a single-pass heater can be used to heat the first reaction solution. Exemplary single-pass heaters include self-rising film evaporators, falling film evaporators, electric heaters, etc. After being rapidly heated to above 200°C by this heater, the solution enters the reactor, where the dehydration and cyclization reaction of 4-HBA is completed.

[0104] In step (3), the reaction temperature is 200-300℃, for example 200-250℃, 200-230℃, or 200-210℃. Controlling the reaction in step (3) within the reaction temperature defined herein can effectively reduce the content of heavy component impurities in step (3), thereby increasing the yield of 2-pyrrolidone. The inventors have found that when the reaction temperature in step (3) exceeds 300℃, the reaction proceeds in the reverse direction, resulting in a decrease in the conversion rate of 4-HBA.

[0105] In step (3), the reaction pressure is 60-80 bar, for example 65 bar, 70 bar, 75 bar, 80 bar, preferably 70-80 bar, 73-78 bar.

[0106] In some embodiments, in step (3), the conversion rate of 4-hydroxybutyramide in the dehydration condensation reaction is ≥99%.

[0107] In some embodiments, in step (3), the yield of 2-pyrrolidone from the dehydration condensation reaction is ≥98%.

[0108] In some embodiments, the content of γ-butyrolactone in the third reaction solution is ≤1.00wt%, preferably ≤0.40wt% or ≤0.30wt%.

[0109] In some embodiments, the content of 4-hydroxybutyramide in the third reaction solution is ≤1.00wt%, preferably ≤0.80wt% or ≤0.40wt%.

[0110] In some embodiments, the residue content in the third reaction solution is ≤2.00wt%, preferably ≤1.50wt%, and more preferably ≤1.00wt%.

[0111] In some embodiments, the content of 4-(N-pyrrolidone)butyramide in the third reaction solution is ≤0.10wt%, preferably ≤0.05wt% or ≤0.02wt%.

[0112] In some embodiments, the content of 2-pyrrolidone in the third reaction solution is ≥57.00 wt%.

[0113] In the method, since the heat loss of the second reaction liquid when it enters the reactor of step (3) from the heater of step (2) is negligible, the temperature of the second reaction liquid is always maintained in the range of 200-300℃.

[0114] Based on the above research results, the method described in this paper is a two-step liquid-phase reaction without a catalyst. The aim is to adopt different control strategies to control the formation of products 4-HBA and PBA in the two-step reaction under mild conditions, so as to minimize the occurrence of side reactions and reduce the formation of heavy component impurities, thereby obtaining high-purity 2-PY products with high yield.

[0115] In some embodiments, the method further includes the step of: (4) subjecting the third reaction liquid to a first distillation for removing light component impurities and a second distillation for removing heavy component impurities in sequence to obtain the 2-pyrrolidone product.

[0116] In some embodiments, the temperature of the first distillation is 150±5℃.

[0117] In some implementations, the pressure of the first distillation is 400 ± 20 kPa.

[0118] In some embodiments, the temperature of the second distillation is 175°C ± 5°C, for example, 175°C ± 2°C.

[0119] In some implementations, the pressure of the second distillation is 5 kPa ± 1.

[0120] The first distillation is used to remove light component impurities from the third reaction solution. These light component impurities may include ammonia, water, and γ-butyrolactone.

[0121] The second distillation is used to remove heavy component impurities from the third reaction solution. These heavy component impurities may include 4-(N-pyrrolidone)butyramide, 4-hydroxybutyric acid, and oligomers of 2-PY. The heavy component impurities separated by the second distillation may also carry a certain amount of 2-pyrrolidone. Therefore, the second distillation process further includes a step of recovering the 2-pyrrolidone mixed in with the heavy component impurities to improve the yield of 2-PY. The recovery method involves recovering the 2-pyrrolidone from the heavy component impurities discharged from the column bottom via a thin-film evaporator. An exemplary recovery pressure may be 3 kPa ± 1. An exemplary recovery temperature may be 160 °C ± 2.

[0122] In the second distillation process, the top of the column typically contains a lower concentration of 2-PY, while the bottom contains heavier impurities. The heavier impurities from the bottom are preferably sent to an evaporator to recover 2-PY. The 2-pyrrolidone product is collected from the middle of the second distillation column used for the second distillation (mid-collection). The location of the mid-collection can be determined based on the calculated number of theoretical trays. In some embodiments, the mid-collection is located at the calculated position corresponding to the 2nd to 5th theoretical trays counted downwards from the top of the column. In some embodiments, the product column 5 has four sections of packing, with the mid-collection located between the first and second sections of packing counted downwards from the top. In some embodiments, the product column 5 has five sections of packing, with the mid-collection located between the second and third sections of packing counted downwards from the top.

[0123] In some embodiments, the 2-pyrrolidone product obtained from the second distillation column has a purity of ≥99%, for example ≥99.5% or ≥99.8%.

[0124] In some implementations, the residue content of the 2-pyrrolidone product obtained from the second distillation column is ≤0.01wt%, for example ≤0.006wt%.

[0125] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Percentages and parts are by weight unless otherwise stated.

[0126] In this article, the methods for detecting the content of each component are as follows: The selectivity of 4-HBA is calculated as: the amount of GBL consumed to generate 4-HBA × 100% / the amount of GBL reactants involved in the reaction.

[0127] The GBL conversion rate is calculated as follows: (Infeed GBL amount - Remaining GBL amount) × 100% / Feed GBL amount.

[0128] The yield of 2-PY is calculated as the actual yield of 2-PY divided by the theoretical yield of 2-PY. The theoretical yield of 2-PY is calculated based on the content of γ-butyrolactone actually added before the start of the reaction in step 1.

[0129] Example 1

[0130] use Figure 1 The apparatus described herein implements the following method for preparing 2-PY.

[0131] Step 1: γ-Butyrolactone and a 70% concentrated ammonia solution (prepared from liquid ammonia and water) were precisely metered, with a molar ratio of GBL:ammonia of 1:1.05. After passing through a static mixer, the mixture was added from the top of a tower reactor with 7 trays. The reaction temperature was 30℃±2°C, and the reaction pressure was 5 bar±0.1 bar. A low-temperature ammonia-nitrogen mixture was added through 5 axially distributed inlets from the top to the bottom of the tower. The ratio of the total molar amount of ammonia and nitrogen in the mixture to the molar amount of GBL was 1:100, and the molar fraction of ammonia in the mixture was 95%. The inlet temperature was maintained at 30±1°C, and the inlet pressure was 15 bar, yielding 4-HBA. The residence time for the reaction in Step 1 was 10 min. After the reaction, the composition and content of the liquid in the bottom of the tower were measured, as shown in Table 1 of Test Example 1.

[0132] Step 2: Add a certain amount of deionized water to the prepared 4-HBA to control the 4-HBA concentration at 70wt%±5. Continuously feed the material into the heater and rapidly heat it to 200℃. The heating time (the time from when the material enters the heater to when it enters the dehydration reactor) is 2 minutes.

[0133] Step 3: A dehydration condensation reaction is carried out at a temperature of 205℃±2°C and a pressure of 75±1 bar. After the reaction in Step 3 is completed, the composition and content of the reaction solution are shown in Table 3 of Test Example 1. The heavy component impurities after the reaction in Step 3 mainly include oligomers of PBA, 4-hydroxybutyric acid, and 2-PY, as well as residues of unknown components.

[0134] Step 4: Post-processing of the distillation section includes first and second distillations. The first distillation removes ammonia, water, and small amounts of light components such as GBL from the 2-PY reaction solution, performing preliminary separation. The operating temperature is 150±5℃, and the operating pressure is 400±20kPa. The light components are collected at the top of the column, while the crude 2-PY from the bottom is sent to the second distillation column. The second distillation is a vacuum column, used to purify the 2-PY after the light components have been removed to obtain the final product. The operating pressure is 5kPaA±1, and the temperature is 175℃±2. The top of the column contains a lower concentration of 2-PY. The final 2-PY product is collected from the middle of the column (between the first and second packing sections from top to bottom; the second distillation column has a total of four packing sections). Heavy impurities, including 2-PY, are discharged from the bottom of the column. These heavy impurities mainly consist of PBA, 4-hydroxybutyric acid, and oligomers of 2-PY. Therefore, the heavy component impurities in the second distillation column are further recovered by a thin-film evaporator to improve the yield of 2-PY. The recovery operation is carried out at a pressure of 3 kPa ± 1 and a temperature of 160 °C ± 2. The product recovered after the second distillation is subjected to chromatographic analysis. The purity of the 2-PY product and the residue content are shown in Table 4 of Test Example 1.

[0135] Example 2

[0136] The same preparation method as in Example 1 was used, except that in step 2, the time for the feed to be heated to 200°C by the heater was controlled to be 1.0 min.

[0137] After the reactions in steps 1 and 3 are completed, the composition and content of the reaction solution are shown in Tables 1 and 3 of Test Example 1. After secondary distillation, the purity of the 2-PY product and the content of the residue are shown in Table 4 of Test Example 1.

[0138] Comparative Example 1

[0139] The same preparation method as in Example 1 was used, the only difference being that the reaction temperature and the inlet temperature of the ammonia-nitrogen mixture in step 1 were controlled at 90°C. The relatively high temperature resulted in a lower 4-HBA content in step 1. Because the 4-HBA concentration in step 1 was too low, no additional water was added to adjust the concentration. At this reaction temperature (90°C), a large amount of ammonia in the liquid phase vaporized, and the higher reaction temperature led to a significant increase in residue.

[0140] After the reactions in steps 1 and 3 are completed, the composition and content of the reaction solution are shown in Tables 1 and 3 of Test Example 1. After secondary distillation, the purity of the 2-PY product and the content of the residue are shown in Table 4 of Test Example 1.

[0141] Comparative Example 2

[0142] The same preparation method as in Example 1 was used, the only difference being that the ammonia-nitrogen mixture was not used for heat removal, and the tower reactor was used only as a conventional adiabatic reactor. Due to the lack of heat removal measures, the temperature gradually increased as the reaction proceeded, and the vaporization of ammonia gradually increased, eventually reaching 81°C at the reactor outlet.

[0143] After the reactions in steps 1 and 3 are completed, the composition and content of the reaction solution are shown in Tables 1 and 3 of Test Example 1. After secondary distillation, the purity of the 2-PY product and the content of the residue are shown in Table 4 of Test Example 1.

[0144] Comparative Example 3

[0145] The same preparation method as in Example 1 was used, except that in step 2, the material discharged from the deammoniation tower was heated to 200°C by a heater and the residence time was 20 minutes.

[0146] After the reaction in step 3 was completed, the composition and content of the reaction solution were shown in Table 3 of Test Example 1. After secondary distillation, the purity of the 2-PY product and the content of the residue were shown in Table 4 of Test Example 1.

[0147] Test Example 1

[0148] In this test, the contents of GBL, 4-HBA, 2-PY, heavy component impurities, and light component impurities other than water were analyzed by chromatography. The instrument model was Thermo Fisher Scientific Trace 1310 dual injection system, and the chromatographic column model was DB-5ms.

[0149] The water content was tested using the Karl Fischer method, and the instrument used was a Mettler volumetric moisture analyzer V30.

[0150] Color numbers were tested using a Lovbond PFXi-195 PH spectrophotometer.

[0151] The ammonia content was analyzed by titration with 0.5 mol / L HCl standard solution. A Mettler Toledo s220 titrator was used.

[0152] The components and their contents in the reaction solution after step 1 are shown in Table 1 below. The conversion rate of γ-butyrolactone and the selectivity of 4-hydroxybutyramide are shown in Table a.

[0153] Table 1

[0154] Table a

[0155] The analysis results of the reaction solution in step 1 from Tables 1 and a show that in Examples 1 and 2, the conversion rate of GBL and the content of 4-HBA were relatively high, while the residue content was low, indicating that the reaction conditions of low temperature and high concentration of ammonia were favorable for the formation of 4-HBA. The experimental results of Comparative Example 1 show that when the reaction temperature was increased to 90℃, a large amount of ammonia in the reaction solution was vaporized, the molar ratio of GBL to NH3 in the liquid phase reaction was approximately 2:1, the conversion rate decreased significantly, and the amount of residue was much greater than in Examples 1 and 2. Similarly, because no heat removal measures were taken in Comparative Example 2, the reaction temperature of the reaction solution increased significantly. In the lower tray of the tower reactor, the ammonia in the liquid phase was severely vaporized, affecting the reaction effect. The ammonia content (calculated by the mass of NH3) and the temperature of the reaction solution in different layers (1#, 2#, 5#) of the tower from the top of Example 1 and Comparative Example 2 are shown in Table 2 below.

[0156] Table 2

[0157] The reaction analysis of ammonia nitrogen removal in Table 2 also shows that heat removal via stripping of the ammonia nitrogen mixture stabilizes the temperature of each tray within the reaction temperature range. In contrast, in Comparative Example 2, without heat removal via the ammonia nitrogen mixture, the temperature rises rapidly as the reaction proceeds. With the increase in temperature, the ammonia vaporization rate increases, and the ammonia concentration in the liquid phase of the tray decreases. The ammonia concentration in the liquid phase at the second and fifth trays is already lower than in Example 1. Combined with the lower GBL conversion rate in Comparative Example 2 shown in Table 1, this indicates that the rapid decrease in ammonia is not due to the progress of the reaction, but rather to ammonia volatilization. After the ammonia concentration decreases, the reaction rate also decreases, and the temperature exhibits a phenomenon of first rising and then falling, eventually reaching equilibrium at a lower conversion rate.

[0158] The components and their contents in the reaction solution after step 3 are shown in Table 3. The conversion rate of 4-hydroxybutyramide and the yield of 2-PY are shown in Table b.

[0159] Table 3

[0160] Table b

[0161] The analysis results of the reaction solution in step 3, as shown in Tables 3 and b, indicate that Examples 1 and 2 effectively reduced the formation of PBA by controlling the heating time to 200°C to within 10 minutes (specifically within 2 minutes), thereby reducing the content of heavy component impurities. Therefore, the residue content in the reaction solution was low. Comparative Example 3 shows that after heating to 200°C for more than 10 minutes, the residue content in the reaction solution increased significantly, far exceeding that of Examples 1 and 2. This demonstrates that controlling the heating time to 200°C is effective in reducing the content of heavy component impurities in the reaction solution after the reaction in step 3.

[0162] The purity and residue content of the 2-PY product obtained from the second distillation column after two distillations in each embodiment and comparative example are shown in Table 4.

[0163] Table 4

[0164] Test Example 2

[0165] 200g of 2-PY prepared in Examples 1-2 and Comparative Examples 1-3 were weighed and placed in a three-necked flask, and 15g of KOH was added to prepare potassium pyrrolidone. The mixture was kept at 90°C for 1 hour under stirring, and the water was removed by vacuum evaporation. The mixture was cooled to 30°C, and 4g of acetyl chloride, the initiator, was added. After a vacuum reaction at 60°C for 60 minutes, the product began to solidify and precipitate. A white solid product was obtained after 24 hours. The separated white solid product was washed with acetone and water, filtered through filter paper, and washed again with water. It was dried in a vacuum oven for 12 hours to obtain pure nylon 4. The obtained sample was subjected to colorimetric testing using a Koncia Minolta CM-5 according to ASTM D1925. The test results are shown in Table 5 below.

[0166] Table 5

Claims

1. An apparatus for preparing 2-pyrrolidone, characterized in that, The apparatus sequentially includes an ammonolysis reaction tower for carrying out the ammonolysis reaction, an ammonia removal tower for removing ammonia from the reaction system, a dehydration reactor for carrying out the dehydration condensation reaction, a light component tower for removing light component impurities, a product tower for removing heavy component impurities, and an evaporator for recovering 2-pyrrolidone from the heavy component impurities; one or more inlets for the ammonia-nitrogen mixture to enter the ammonolysis reaction tower are provided on the outer wall of the ammonolysis reaction tower.

2. The apparatus for preparing 2-pyrrolidone as described in claim 1, characterized in that, A temperature control point is provided at the feed inlet of the dehydration reactor; The device includes a feed inlet for ammonia and γ-butyrolactone to enter the device; The top of the ammonium hydrolysis reaction tower is provided with a top exhaust port for discharging the ammonia-nitrogen mixture from the ammonium hydrolysis reaction tower. The bottom of the ammonium hydrolysis reaction tower is equipped with a bottom outlet for discharging the reaction liquid from the ammonium hydrolysis reaction tower. The ammonia removal tower is provided with a top outlet and a top inlet at the top. The ammonia removal tower is equipped with a tower outlet and a low-pressure steam inlet for introducing low-pressure steam into the ammonia removal tower. A heater is installed on the pipeline connecting the ammonia removal tower and the dehydration reactor; The light component tower is equipped with a top discharge port and a top feed port at the top. The reboiler of the light component column is equipped with a reboiler outlet and a reboiler inlet; The area between the top feed inlet of the light component tower and the bottom feed inlet of the light component tower is provided with a first feed inlet connected to the dehydration reactor and a second feed inlet for the recovery of product feed. The top of the product tower is equipped with a top discharge port and a top feed port; The product tower is equipped with a tower outlet and a tower inlet; The area between the top inlet and the bottom inlet of the product tower is provided with a product outlet for discharging the 2-pyrrolidone product from the device and an inlet for connecting to the light component tower.

3. The apparatus for preparing 2-pyrrolidone as described in claim 2, characterized in that, The feed inlet of the device is connected to the feed inlet of the ammonium hydrolysis reaction tower via a feed mixer and a feed preheater. The exhaust port at the top of the ammonium hydrolysis reaction tower is connected to the inlet of the ammonia water collection tank through the condenser at the top of the ammonium hydrolysis tower. The bottom outlet of the ammonolysis reaction tower is connected to the inlet of the ammonia removal tower; The top outlet of the ammonia removal tower is connected to the inlet of the top condenser of the ammonia removal tower, and the first outlet of the top condenser of the ammonia removal tower is connected to the top inlet of the ammonia removal tower. The outlet of the deammoniation tower is connected to the dehydration reactor; A heat exchanger is installed on the pipeline connecting the ammonia removal tower and the heater; The top outlet of the light component column is connected to the light component column reflux tank through the top condenser of the light component column. The bottom outlet of the light component column is connected to the inlet of the light component column reboiler, and the outlet of the light component column reboiler is connected to the bottom outlet of the light component column. The bottom outlet of the light component tower is connected to the product tower; The product outlet of the product tower is connected to the product cooler; The top outlet of the product tower is connected to the product tower reflux tank via the top condenser of the product tower, and the bottom outlet of the product tower reflux tank is connected to the top inlet of the product tower. The product column bottom outlet is connected to the product column reboiler inlet, and the product column reboiler outlet is connected to the product column bottom inlet. The product tower's bottom outlet is connected to the evaporator; The evaporator is provided with a bottom outlet for discharging residue from the device and a top outlet for returning the recovered 2-pyrrolidone product to the light component tower.

4. The apparatus for preparing 2-pyrrolidone as described in claim 1, characterized in that, The inlets for the ammonia-nitrogen mixture to enter the ammonia decomposition reaction tower are equidistantly arranged in the extending direction of the ammonia decomposition reaction tower. The ammonium decomposition reaction tower is equipped with multiple trays. The inlet for the ammonia-nitrogen mixture to enter the ammonium decomposition reaction tower is located in the middle of two adjacent trays. The inlet for the ammonia-nitrogen mixture to enter the ammonium decomposition reaction tower is optionally located below the bottom tray.

5. The apparatus for preparing 2-pyrrolidone as described in claim 3, characterized in that, The ammonia water collection tank is provided with a top outlet, which is connected to the inlet of the ammonia nitrogen mixture on the ammonia decomposition reaction tower through an ammonia nitrogen circulating gas fan and an ammonia nitrogen circulating gas cooler. The bottom outlet of the ammonia collection tank is connected to the feed inlet of the device.

6. The apparatus for preparing 2-pyrrolidone as described in claim 5, characterized in that, The pipeline connecting the ammonia water collection tank and the ammonium hydrolysis reaction tower is also equipped with a nitrogen inlet for fresh nitrogen to enter the device; The top outlet of the ammonia collection tank is also connected to a pipeline for discharging a mixture of ammonia and nitrogen gas from the device.

7. The apparatus for preparing 2-pyrrolidone as described in claim 3, characterized in that, The top condenser of the ammonia removal tower is also provided with a second discharge port for discharging ammonia water from the device. The top outlet of the product tower reflux tank is connected to a pipeline for discharging non-condensable gases from the device.

8. The apparatus for preparing 2-pyrrolidone as described in claim 3, characterized in that, The bottom outlet of the deammoniation tower is connected to the first inlet of the heat exchanger, and the first outlet of the heat exchanger is connected to the inlet of the heater. The outlet of the dehydration reactor is connected to the second inlet of the heat exchanger, and the second outlet of the heat exchanger is connected to the light component tower.

9. The apparatus for preparing 2-pyrrolidone as described in claim 3, characterized in that, The light component tower reflux tank is equipped with a top inlet connected to the top discharge port of the light component tower, a top outlet for discharging non-condensable gases, and a bottom outlet for discharging liquid materials from the light component tower reflux tank. The bottom outlet of the reflux tank of the light component tower is connected to the top feed inlet of the light component tower; The top outlet of the light component tower reflux tank is connected to a pipeline for discharging non-condensable gases from the device; The pipeline connecting the top feed inlet of the light component tower to the bottom outlet of the light component tower reflux tank is also equipped with a pipeline for discharging light component impurities from the device.

10. The apparatus for preparing 2-pyrrolidone as described in claim 2, characterized in that, The top outlet of the evaporator is connected to the recycled product collection tank via the evaporator condenser, and the outlet of the recycled product collection tank is connected to the second inlet of the light component tower.

Images