A method and reaction system for the continuous production of lactam monomers

Abstract

The application discloses a kind of continuous production lactam monomer method and reaction system, two-stage reactor is divided into heat exchange zone and reaction zone from top to bottom in it, the heat exchange zone is equipped with packing or tray, the bottom of the reaction zone is equipped with vapor generator;Raw material containing amino acid and low carbon alcohol are entered into two-stage reactor from top, wherein, amino acid is dehydrated and cyclized to generate lactam monomer.The reaction system includes two-stage reactor and alcohol recovery column, two-stage reactor is used for amino acid dehydration and cyclization reaction to generate lactam monomer, and the alcohol recovery column is used to recover low carbon alcohol in reaction material.The continuous production lactam monomer method and reaction system provided by the application can effectively reduce the amount of low carbon alcohol in reactor inlet material, and further reduce the energy consumption of alcohol recovery column.

Description

Technical Field

[0001] This invention relates to a method for the continuous production of organic chemical monomers, and more specifically, to a method and a continuous production reaction apparatus for the intramolecular dehydration cyclization of amino acids to prepare lactam monomers. Background Technology

[0002] Amino acids are organic compounds containing a basic amino group and an acidic carboxyl group. They are formed when the hydrogen atom on the carbon atom of a carboxylic acid is replaced by an amino group. Amino acids obtained from the hydrolysis of biological proteins are all α-amino acids. Because the acidic and basic groups present within an amino acid molecule can interact to form an inner salt, amino acids usually exist as dipolar ions. Amino acid molecules can undergo intermolecular dehydration to form polypeptides. For some amino acids containing multiple amino or carboxyl groups, such as lysine, glutamic acid, glutamine, arginine, and ornithine, intramolecular dehydration cyclization can also occur under specific conditions to generate certain cyclic compounds, exhibiting reaction advantages unmatched by conventional organic synthesis.

[0003] Aminocaprolactam is a widely used organic monomer, serving as a food additive, a raw material for the production of caprolactam (a precursor to nylon-6 and nylon-12), and an important pharmaceutical intermediate. Currently, commercially available aminocaprolactam monomers are mainly obtained from cyclohexene via addition, amination, and Beckmann rearrangement. This process involves long reaction routes, complex processes, and the use of various toxic and harmful substances, severely limiting its large-scale production and application. The latest route for aminocaprolactam preparation utilizes lysine from biomass fermentation. Patent CN111116472A discloses a method for preparing aminocaprolactam from lysine via esterification followed by dehydration cyclization. This method requires large amounts of strong acids and bases, produces a large amount of inorganic salts as byproducts, and has a low yield of only about 40%. CN102093292A discloses a method for synthesizing aminocaprolactam, which involves a nucleophilic substitution reaction between α-halocaprolactam and benzylamine under certain conditions, followed by hydrogenolysis to remove the benzyl group and generate the target aminocaprolactam. The above synthesis process requires two different reactions, resulting in low process selectivity and affecting product yield. A one-step method refers to the direct synthesis of aminocaprolactam from lysine, first reported in the literature [Tetrahedron Letters, 1980, 21, 2443-2446]. Lysine undergoes dehydration and cyclization in toluene in the presence of silica gel or alumina to generate aminocaprolactam, with a product yield of 37%-71%. Patent JPS5976063A discloses a method for the dehydration and cyclization of lysine to generate aminocaprolactam in a specific alcohol without a catalyst. The alcohol is a C4-C8 aliphatic or alicyclic alcohol, such as butanol, decanol, 2-ethylhexanol, cyclopentanol, etc. JP2012162463A reports a simple and efficient method for the direct production of aminocaprolactam from lysine. The raw material lysine can be obtained from the enzymatic reaction of biomass such as waste molasses. The preferred reaction temperature is 200-350℃; the reaction is carried out in an inert gas atmosphere, and the preferred reaction pressure is 3-10 MPa. Patent CN102718711A discloses a method for preparing aminocaprolactam hydrochloride, which uses D-lysine monohydrochloride or D-lysine as raw material, sodium hydroxide as base, and n-hexanol as solvent, and reacts under reflux conditions at 155-157℃ to obtain aminocaprolactam product.

[0004] The above preparation method realizes the possibility of synthesizing aminocaprolactam from lysine in biomass along the reaction pathway. However, due to the characteristics of the reaction itself, namely the competitive relationship between intramolecular dehydration and intermolecular dehydration, the yield of the target product aminocaprolactam is usually not high, and there are many and mixed by-products, which not only reduces the effective utilization rate of raw materials, but also has a significant impact on the subsequent product separation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and reaction system for continuous production of lactam monomers, such as a continuous production method and reaction system for synthesizing aminocaprolactam monomers using lysine as a raw material, and to achieve the purpose of improving reaction selectivity and reducing process energy consumption.

[0006] In a first aspect, the present invention provides a method for continuous production of lactam monomers, wherein a two-stage reactor is divided into a heat exchange zone and a reaction zone from top to bottom, wherein the heat exchange zone is equipped with packing or trays, and the bottom of the reaction zone is equipped with a steam generator; a raw material containing amino acids and a low alcohol enter the two-stage reactor from the top and discharge the reaction post-flow from the bottom, wherein the amino acids are dehydrated and cyclized to generate lactam monomers.

[0007] In this invention, the height ratio of the heat exchange zone to the reaction zone in the two-stage reactor is 0.02-0.3:1, preferably 0.05-0.2:1.

[0008] Preferably, a liquid level detection element is provided at the top of the reaction zone, which automatically controls the liquid phase state of the reaction zone by being linked with the outlet valve at the bottom.

[0009] In this invention, the amino acid molecule contains multiple amino or carboxyl groups. In a low-carbon alcohol, the amino and carboxyl groups within the amino acid molecule undergo dehydration and cyclization to generate a lactam monomer. Preferably, the amino acid is lysine, and the raw material containing the amino acid is selected from one or more of lysine, lysine salt, and lysine aqueous solution; more preferably, it is a 1wt%-60wt% lysine aqueous solution. Optionally, the lysine aqueous solution is a lysine aqueous solution obtained through bio-fermentation.

[0010] In this invention, the lower alcohols are C1-C5 alcohols. These lower alcohols have a lower boiling point than water, or can form low-boiling-point azeotropes with water.

[0011] Preferably, the lower alcohol is selected from one or more of methanol, ethanol, propanol, sec-butanol, tert-butanol, n-butanol, isobutanol, n-pentanol, and isopentanol.

[0012] Optionally, the molar ratio of low alcohol to amino acid molecules in the reaction feed is (2-80):1, preferably (5-60):1, and more preferably (10-40):1.

[0013] In this invention, in the two-stage reactor, the operating conditions of the reaction zone are as follows: temperature is 140-300℃, preferably 150-250℃; pressure is the bubble point pressure of the material at the reaction temperature; and the residence time of the raw material containing amino acids in the reaction zone is 0.5-6.0h, preferably 1.0-4.0h.

[0014] Preferably, the bottom discharge of the two-stage reactor enters the alcohol recovery tower, the bottom of the alcohol recovery tower collects a solution rich in lactam monomers, and the top of the tower collects alcohol or alcohol-water azeotrope and returns it to the two-stage reactor.

[0015] The alcohol recovery tower is a packed tower or a plate tower, with an operating pressure of 0.02-0.5 MPa, a bottom temperature of 60-160℃, and a reflux ratio of 0.5-3.0. The pressure mentioned refers to absolute pressure.

[0016] Secondly, the present invention provides a reaction system for continuous production of lactam monomers, comprising a two-stage reactor and an alcohol recovery tower. The two-stage reactor is used for the dehydration and cyclization reaction of amino acids to generate lactam monomers, and is divided into a heat exchange zone and a reaction zone from top to bottom. The heat exchange zone is equipped with packing or trays, and the top of the heat exchange zone is equipped with a raw material inlet and a low-carbon alcohol inlet. The bottom of the reaction zone is equipped with a steam generator and a bottom material outlet. The alcohol recovery tower is used to recover low-carbon alcohols from the reactants, and is equipped with an inlet, a top material outlet, and a bottom material outlet. The bottom material outlet of the two-stage reactor is connected to the inlet of the alcohol recovery tower, and the top material outlet of the alcohol recovery tower is connected to the low-carbon alcohol inlet of the tower reactor.

[0017] Preferably, the reaction system further includes a product separation tower for separating lactam monomers from the lactam mixture. The product separation tower has an inlet, a top material outlet, and a bottom material outlet. The bottom material outlet of the alcohol recovery tower is connected to the inlet of the product separation tower.

[0018] The beneficial effects of the continuous production method and reaction system for lactam monomers provided by this invention are as follows:

[0019] The method provided by this invention uses a two-stage reactor for the dehydration and cyclization reaction of amino acids. Low-carbon alcohol vapor is generated by a steam generator at the bottom of the two-stage reactor, which allows some of the low-carbon alcohol to circulate in the reaction zone. This can effectively increase the low-carbon alcohol load in the reaction zone, thereby reducing the amount of low-carbon alcohol in the reaction feed and output materials and reducing the energy consumption of the equipment.

[0020] A heat exchange zone is set up in the two-stage reactor, and the rising steam in the reaction zone is used to preheat the raw materials containing amino acids. The heat of the device is recovered with high heat exchange efficiency, further reducing the energy consumption of the device. Attached Figure Description

[0021] Figure 1 A schematic flowchart of the continuous production method of lactam monomers provided by the present invention.

[0022] in:

[0023] I-Heat Exchange Zone II-Reaction Zone

[0024] 1- Raw materials containing amino acids 2- Low-carbon alcohols 3- Two-stage reactor

[0025] 4-Steam generator; 5-Level detection element; 6-Level control valve

[0026] 7-Alcohol recovery tower 8-Reaction discharge Detailed Implementation

[0027] The specific embodiments of the present invention are described in detail below.

[0028] In this application, the terms "upper part," "lower part," and "bottom" are all based on the relative positional relationship of the container or component. Specifically, "bottom" refers to the position of the container from bottom to top at 0-10%, "lower part" refers to the position of the container from bottom to top at 0-50%, "upper part" refers to the position of the container from bottom to top at 50-100%, and "top" refers to the position of the container from bottom to top at 90-100%.

[0029] In this application, all pressures mentioned refer to absolute pressures.

[0030] This invention provides a method for continuous production of lactam monomers. The two-stage reactor is divided into a heat exchange zone and a reaction zone from top to bottom. The heat exchange zone is equipped with packing or trays, and the bottom of the reaction zone is equipped with a steam generator. The raw material containing amino acids and low alcohols enter the two-stage reactor from the top. The amino acids are dehydrated and cyclized to generate lactam monomers. The reaction stream is discharged from the bottom.

[0031] Using amino acids as raw materials and low-carbon alcohols as auxiliaries, intramolecular dehydration cyclization of amino acids occurs within the two-stage reactor to generate lactam compounds. The amino acid molecule contains multiple amino or carboxyl groups; the intramolecular dehydration cyclization refers to the reaction of the amino and carboxyl groups within the amino acid molecule to generate lactam compounds. Lysine is preferably used as the amino acid, but other amino acids containing multiple amino or carboxyl groups, such as glutamic acid, arginine, and other amino acid molecules with similar structures, are also suitable for this method. Preferably, the raw material containing amino acids is selected from one or more of lysine, lysine salts, and aqueous solutions of lysine. Optionally, the aqueous solution of lysine is an aqueous solution of lysine obtained through bio-fermentation, with a lysine mass fraction of 1 wt%-60 wt%.

[0032] The amino acid-containing raw material and the low-carbon alcohol can be mixed and then fed into a two-stage reactor together, or they can be fed into the two-stage reactor separately. In one embodiment, the amino acid-containing raw material and the circulating low-carbon alcohol are mixed and then enter the heat exchange zone of the two-stage reactor from the top. After flowing downwards and undergoing heat exchange and temperature rise, they enter the reaction zone, where the amino acid undergoes a cyclization and dehydration reaction to obtain an aminoamide monomer.

[0033] In this invention, the low-carbon alcohol refers to C1-C5 fatty alcohols, which have a lower boiling point than water or can form a low-boiling-point azeotrope with water. Preferably, the low-carbon alcohol is selected from one or more of methanol, ethanol, propanol, sec-butanol, tert-butanol, n-butanol, isobutanol, n-pentanol, and isopentanol. The molar ratio of low-carbon alcohol to amino acid in the reaction feed is (2-80):1, preferably (5-60):1, and more preferably (10-40):1.

[0034] In this invention, the operating conditions of the two-stage reactor are as follows: the temperature of the reaction zone is 140-300℃, preferably 150-250℃; the pressure is the bubble point pressure of the material at the reaction temperature; the residence time of the amino acid-containing raw material in the reaction zone is 0.5-6.0h, preferably 1.0-4.0h. The top temperature of the heat exchange zone is 30-60℃.

[0035] In this invention, the operating pressure of the two-stage reactor is the bubble point pressure of the reaction system at the reaction temperature. This bubble point pressure is related to the lower alcohols in the reaction system and also to the reaction temperature. For example, at a reaction temperature of 150–200°C, the bubble point pressure of methanol is 1.3–4.0 MPa; at a reaction temperature of 150°C, the bubble point pressure of the low-boiling-point azeotrope formed by isobutanol and water is 0.59 MPa; and at a reaction temperature of 250°C, the bubble point pressure of the low-boiling-point azeotrope formed by isobutanol and water is 5.3 MPa.

[0036] In this invention, the two-stage reactor consists of a heat exchange zone and a reaction zone, which can share a single cylindrical structure or be installed separately. Preferably, a liquid level detection element is installed at the top of the reaction zone. This element controls the bottom outlet valve of the reactor, automatically controlling the liquid level in the reaction zone and maintaining its liquid phase state. A steam generator, selected from thermosiphon, autoclave, or built-in coil type, is installed at the bottom of the reaction zone; it can also be used for direct heating with hot steam. The heat exchange zone is filled with packing or trays, allowing the reaction feed to directly contact the steam from the reaction zone from top to bottom for mass and heat transfer.

[0037] In a preferred embodiment, the bottom discharge of the two-stage reactor enters an alcohol recovery tower. The bottom of the alcohol recovery tower yields an aqueous solution rich in lactam monomers, while the top of the tower yields an alcohol or alcohol-water azeotrope that is recycled back to the two-stage reactor. The alcohol recovery tower can be a packed tower or a plate tower, with an operating pressure of 0.02-0.5 MPa, a bottom temperature of 60-160°C, and a reflux ratio of 0.5-3.0.

[0038] This invention provides a reaction system for continuous production of lactam monomers, comprising a two-stage reactor and an alcohol recovery tower. The two-stage reactor is used for the dehydration and cyclization reaction of amino acids to generate lactam monomers, and is divided into a heat exchange zone and a reaction zone from top to bottom. The heat exchange zone is equipped with packing or trays, and the top of the heat exchange zone has a raw material inlet and a low-carbon alcohol inlet. The bottom of the reaction zone has a steam generator and a bottom material outlet. The alcohol recovery tower is used to recover low-carbon alcohols from the reactants, and has an inlet, a top material outlet, and a bottom material outlet. The bottom material outlet of the two-stage reactor is connected to the inlet of the alcohol recovery tower, and the top material outlet of the alcohol recovery tower is connected to the low-carbon alcohol inlet of the tower reactor.

[0039] Optionally, in the two-stage reactor, the height ratio of the heat exchange zone to the reaction zone is (0.02-0.3):1, preferably (0.05-0.2):1. Preferably, a liquid level detection element is provided at the top of the reaction zone, and an outlet valve is provided at the bottom material outlet of the reactor. The liquid level detection element is linked to the outlet valve to automatically control the liquid level in the reaction zone.

[0040] The following detailed description, with reference to the accompanying drawings, uses the continuous production of aminocaprolactam from lysine using methanol as an adjuvant as an example to illustrate specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0041] Appendix Figure 1 A schematic flow chart of the continuous production method of lactam monomers provided by the present invention is attached. Figure 1 As shown, a lysine aqueous solution 1 and recycled methanol 2, in a specific ratio, enter the two-stage reactor 3 from the top. They flow downwards through heat exchange zone I of the reactor 3 and directly contact the rising steam from reaction zone II for mass and heat transfer. The raw material is heated to the reaction temperature by the steam and then enters reaction zone II, while the rising steam is condensed and returned to reaction zone II. In reaction zone II, lysine reacts further with the aid of methanol to produce aminocaprolactam. Part of the reacted material is heated by steam generator 4, where the low-boiling-point methanol vaporizes and returns to reaction zone II. The remaining material enters the alcohol recovery tower 7 via level control valve 6. The opening of the level control valve is interlocked with the level detection element 5 at the top of reaction zone II. Recycled methanol 2 is collected from the top of the alcohol recovery tower 7 and returned to the inlet of the two-stage reactor 3. The reaction product 8 collected from the bottom of the tower is an aminocaprolactam aqueous solution, which is sent to the subsequent separation unit to obtain the target product, aminocaprolactam.

[0042] The present invention will be further illustrated by the following examples. However, the present invention is not limited thereto.

[0043] In the comparative examples and embodiments, the lysine aqueous solution was derived from the stock solution of the bio-fermentation process (purchased from Meihua Biotechnology Group Co., Ltd.), and the methanol and ethanol were commercially available products.

[0044] The contents of lysine and aminocaprolactam in the material were analyzed by external standard method of liquid chromatography.

[0045] The reaction conversion rate X and selectivity S are calculated by the following formula:

[0046]

[0047]

[0048] Comparative Example 1

[0049] Comparative Example 1 uses a conventional tubular reactor to dehydrate lysine to prepare aminocaprolactam.

[0050] Lysine aqueous solution and methanol enter the tubular reactor from the bottom, mix and react inside the tubular reactor, and the reacted material exits the reactor from the top.

[0051] The lysine aqueous solution contains 60 wt% lysine, with the remainder being water. The molar ratio of methanol to lysine in the feed is 30:1. The material is fed from the bottom and discharged from the top in a tubular reactor. The reaction temperature is 180℃, the reaction pressure is 3.6 MPa, and the apparent residence time of the reactants in the reactor is 2 hours. Methanol is recovered from the reactants using a packed tower.

[0052] The contents of lysine and aminocaprolactam in the raw materials and reactants were analyzed, and the results of the calculated reaction selectivity and conversion rate are shown in Table 1. The operating conditions of the methanol recovery tower and the heating amount in the reboiler are shown in Table 2.

[0053] Examples 1-2 illustrate the effects of the continuous production method for lactam monomers of the present invention.

[0054] Example 1

[0055] As shown in the attached document Figure 1 The method for continuous production of caprolactam monomer shown in the appendix is ​​as follows. Figure 1 As shown, the two-stage reactor is divided into heat exchange zone I and reaction zone II from top to bottom, with a height ratio of 0.08:1. The heat exchange zone is filled with structured packing.

[0056] Lysine aqueous solution 1 and recycled methanol 2 enter the two-stage reactor 3 from the top, flowing downwards through heat exchange zone I of the reactor 3. The temperature at the top of the heat exchange zone is 50.2℃. The raw materials undergo heat and mass transfer with the rising steam, and after being heated to the reaction temperature by the rising steam, they enter reaction zone II. In reaction zone II, lysine undergoes dehydration and cyclization to produce aminocaprolactam. The liquid level detection element 5 at the top of reaction zone II controls the opening of the outlet valve, automatically maintaining a liquid phase state in reaction zone II. The reacted material enters the alcohol recovery tower 7 through the liquid level control valve 6. Recycled methanol 2 is collected from the top of the alcohol recovery tower 7 and returned to the inlet of the two-stage reactor 3. The reaction product 8 collected from the bottom of the tower is an aminocaprolactam aqueous solution.

[0057] The raw materials used were the same as those in Comparative Example 1, and the reactor feed ratio is shown in Table 1. The apparent residence time of the materials in the reaction zone was 2 hours, and the reaction pressure was 2.5 MPa. The steam generator was a vertical thermosiphon. The lysine content and aminocaprolactam content in the raw materials and the reactants were analyzed, and the results of the calculated reaction selectivity and conversion rate are shown in Table 1. The operating conditions of the two-stage reactor and the methanol recovery tower are shown in Table 2.

[0058] Example 2

[0059] The reaction process, experimental methods, and lysine raw materials were the same as in Example 1, except that the height ratio of the heat exchange zone to the reaction zone was 0.12:1, and a gas-liquid mass transfer sieve plate was installed in the heat exchange zone. Ethanol was used as the low-carbon alcohol auxiliary. The material ratios and reaction results are shown in Table 1, and the reaction operating conditions and energy consumption are shown in Table 2.

[0060] Table 1. Composition of reactants and reaction results

[0061]

[0062] Table 2 Operating conditions of the two-stage reactor and alcohol recovery tower

[0063]

Claims

1. A method for continuous production of lactam monomers, characterized in that, The two-stage reactor is divided into a heat exchange zone and a reaction zone from top to bottom. The heat exchange zone is equipped with packing or trays, and the reaction zone is equipped with a steam generator at the bottom. The raw material containing amino acids and low-carbon alcohols enter the two-stage reactor from the top and flow from top to bottom through the heat exchange zone. They directly contact the rising steam from the reaction zone for mass and heat transfer. The raw material is heated to the reaction temperature by the steam and then enters the reaction zone. At the same time, the rising steam is condensed and returned to the reaction zone. The amino acids undergo dehydration and cyclization to generate lactam monomers. Part of the reacted material is heated by the steam generator, in which the low-boiling-point low-carbon alcohols are vaporized and returned to the reaction zone. The other part is discharged from the bottom of the two-stage reactor into the alcohol recovery tower. The bottom of the alcohol recovery tower is collected as a solution rich in lactam monomers, and the top of the tower is collected as a low-carbon alcohol or alcohol-water azeotrope, which is recycled back to the two-stage reactor.

2. The method for continuous production of lactam monomers according to claim 1, characterized in that, In the two-stage reactor, the height ratio of the heat exchange zone to the reaction zone is 0.02-0.3:

1.

3. The method for continuous production of lactam monomers according to claim 2, characterized in that, In the two-stage reactor, the height ratio of the heat exchange zone to the reaction zone is 0.05-0.2:

1.

4. The method for continuous production of lactam monomers according to claim 1, characterized in that, The reaction zone is equipped with a liquid level detection element at the top, which automatically controls the reaction zone to be in a liquid phase state by being linked with the outlet valve at the bottom.

5. The method for continuous production of lactam monomers according to any one of claims 1-4, characterized in that, The raw material containing amino acids is selected from one or more of lysine, lysine salts, and aqueous solutions of lysine.

6. The method for continuous production of lactam monomers according to claim 5, characterized in that, The raw material containing amino acids is a 1wt%-60wt% lysine aqueous solution.

7. The method for continuous production of lactam monomers according to any one of claims 1-4, characterized in that, The low-carbon alcohols mentioned are selected from C1-C5 alcohols.

8. The method for continuous production of lactam monomers according to claim 7, characterized in that, The lower alcohols mentioned are selected from one or more of methanol, ethanol, propanol, sec-butanol, tert-butanol, n-butanol, isobutanol, n-pentanol, and isopentanol.

9. The method for continuous production of lactam monomers according to any one of claims 1-4, characterized in that, The molar ratio of low alcohols to amino acids in the reaction feed is (2-80):

1.

10. The method for continuous production of lactam monomers according to claim 9, characterized in that, The molar ratio of low alcohols to amino acids in the reaction feed is (5-60):

1.

11. The method for continuous production of lactam monomers according to claim 10, characterized in that, The molar ratio of low alcohols to amino acids in the reaction feed is (10-40):

1.

12. The method for continuous production of lactam monomers according to any one of claims 1-4, characterized in that, In the two-stage reactor, the temperature in the reaction zone is 140-300℃; the pressure is the bubble point pressure of the material at the reaction temperature; and the residence time of the raw material containing amino acids in the reaction zone is 0.5-6.0h.

13. The method for continuous production of lactam monomers according to claim 12, characterized in that, The temperature in the reaction zone of the two-stage reactor is 150-250℃; the residence time of the raw materials containing amino acids in the reaction zone is 1.0-4.0h.

14. The method for continuous production of lactam monomers according to any one of claims 1-4, characterized in that, The alcohol recovery tower is a packed tower or a plate tower, with an operating pressure of 0.02-0.5 MPa, a bottom temperature of 60-160℃, and a reflux ratio of 0.5-3.

0.

15. A reaction apparatus for continuous production of lactam monomers, characterized in that, A method for continuous production of lactam monomers according to any one of claims 1-14, comprising a two-stage reactor and an alcohol recovery tower, wherein the two-stage reactor is used for the dehydration and cyclization reaction of amino acids to generate lactam monomers, and is divided into a heat exchange zone and a reaction zone from top to bottom; the heat exchange zone is equipped with packing or trays, and the upper part of the heat exchange zone is equipped with a raw material inlet and a low-carbon alcohol inlet; the bottom of the reaction zone is equipped with a steam generator and a bottom material outlet; the alcohol recovery tower is used to recover low-carbon alcohols from the reaction material, and is equipped with an inlet, a top material outlet and a bottom material outlet; the bottom material outlet of the two-stage reactor is connected to the inlet of the alcohol recovery tower, and the top material outlet of the alcohol recovery tower is connected to the low-carbon alcohol inlet of the tower reactor.

16. The reaction apparatus for continuous production of lactam monomers according to claim 15, characterized in that, The reaction system further includes a product separation tower, which is used to separate lactam monomers from the lactam mixture. The product separation tower has an inlet, a top material outlet, and a bottom material outlet. The bottom material outlet of the alcohol recovery tower is connected to the inlet of the product separation tower.

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