A continuous process and system for the production of a lactam monomer

Abstract

The application discloses a kind of continuous production method and reaction system of lactam monomer, raw material containing amino acid, with low carbon alcohol into tower reactor, under distillation condition, amino acid is dehydrated and cyclized to generate lactam monomer, discharge into alcohol recovery column in tower reactor bottom, low carbon alcohol obtained from alcohol recovery column is recycled back to tower reactor and recycled, the rest material is further separated to obtain lactam monomer;Wherein, the boiling point of the low carbon alcohol is lower than water, or can form low-boiling azeotrope with water.The reaction system includes tower reactor and alcohol recovery column, wherein the tower reactor is used for the dehydration and cyclization reaction of amino acid to generate lactam monomer;Alcohol recovery column is used to recover low carbon alcohol in reaction material.The continuous production method of lactam monomer provided by the application has the advantages of high reaction selectivity, low process energy consumption and the like.

Description

Technical Field

[0001] This invention relates to an apparatus and method for preparing lactam organic chemical monomers by intramolecular dehydration cyclization of an amino acid containing multiple amino or carboxyl groups, which belongs to the field of reaction process enhancement technology in organic synthesis. 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. 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, in which α-halocaprolactam undergoes a nucleophilic substitution reaction with benzylamine under certain conditions, followed by hydrogenolysis of the benzyl group to 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%. JPS5976063A discloses a method for the dehydration and cyclization of lysine in a specific alcohol without a catalyst to generate aminocaprolactam. 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 waste such as molasses. The preferred reaction temperature is 200–350°C; the reaction is carried out in an inert gas atmosphere, and the preferred reaction pressure is 3–10 MPa. 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 the continuous production of lactam monomers using amino acids, such as a method and system for the continuous production of aminocaprolactam from lysine, so as to achieve continuous production, improve reaction selectivity and reduce process energy consumption.

[0006] In a first aspect, the present invention provides a continuous production method for lactam monomers, wherein a raw material containing amino acids and a low-carbon alcohol are fed into a tower reactor, and the amino acids are dehydrated and cyclized under distillation conditions to generate lactam monomers. The material discharged from the bottom of the tower reactor enters an alcohol recovery tower, and the low-carbon alcohol separated by the alcohol recovery tower is returned to the tower reactor for recycling. The remaining materials are further separated to obtain lactam monomers. The low-carbon alcohol has a lower boiling point than water, or can form a low-boiling-point azeotrope with water.

[0007] 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;

[0008] Preferably, the raw material containing amino acids is a 1wt% to 60wt% aqueous solution of lysine.

[0009] In this invention, the low-carbon alcohol is selected from one or more of methanol, ethanol, propanol and butanol.

[0010] Preferably, in the feed to the tower reactor, the molar ratio of the low-carbon alcohol to the amino acid is (2-80):1, more preferably (5-60):1, and even more preferably (10-40):1.

[0011] Preferably, the reaction temperature in the tower reactor is 140–300°C, more preferably 150–250°C; the pressure at the top of the tower is the bubble point pressure of the low-boiling-point substance or low-azeotropic substance in the system at the actual reaction temperature; the residence time of the raw material containing amino acids in the tower reactor is 0.5–6.0 h, more preferably 1.0–4.0 h.

[0012] In this invention, the alcohol recovery tower is used to recover alcohols or low-carbon alcohol-water azeotropic mixtures from the reaction products, and can be configured as one distillation tower or multiple distillation towers connected in series. Preferably, the operating conditions of the alcohol recovery tower are: operating pressure of -0.08 to 0.5 MPa, bottom temperature of 60 to 160°C, and reflux ratio of 0.5 to 3.0.

[0013] Preferably, the vapor phase collected from the top of the tower reactor is used as a heat source for the reboiler in the bottom of the alcohol recovery tower. After further heat exchange, it is condensed into a liquid phase and then returned to the top of the tower reactor in a total reflux manner.

[0014] In this invention, the tower reactor is a packed tower or a plate tower, preferably a plate tower.

[0015] Preferably, the bottom of the alcohol recovery tower collects a mixed solution of lactam monomers, which refers to an aqueous solution or an alcoholic solution of lactam monomers. This solution is further separated to obtain the lactam monomer product. The top of the tower collects a low-carbon alcohol or an azeotrope of low-carbon alcohol and water. The low-carbon alcohol or the alcohol-water azeotrope is returned to the high-pressure tower reactor for recycling.

[0016] Secondly, the present invention provides a continuous production system for lactam monomers, comprising a tower reactor and an alcohol recovery tower. The tower reactor is provided with a raw material inlet, a low-carbon alcohol inlet, and a bottom material outlet for the dehydration and cyclization reaction of amino acids to generate lactam monomers. The alcohol recovery tower is provided with an inlet, a top material outlet, and a bottom material outlet for the recovery of low-carbon alcohols from the reactants. The bottom material outlet of the tower 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 continuous production system for lactam monomers 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.

[0018] Compared with the prior art, the advantages of the continuous production method and production system for lactam monomers provided by the present invention are as follows:

[0019] (1) The intramolecular dehydration cyclization reaction of amino acids is enhanced by using a tower reactor. The high-load low-carbon alcohol auxiliaries circulating in the tower reactor can effectively improve the selectivity of intramolecular dehydration of amino acids, reduce the occurrence of side reactions, and thus improve the utilization rate of raw materials.

[0020] (2) The tower reactor and the alcohol recovery tower are thermally coupled to realize the effective utilization of heat in the system and reduce process energy consumption. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of one implementation method for the continuous production of lactam monomers.

[0022] Figure 2 This is a schematic diagram of a second embodiment of a continuous production method for lactam monomers.

[0023] in:

[0024] 1- Raw material containing amino acids 2- Heat exchanger 3- Reactor feed

[0025] 4-Tower reactor; 5-Top vapor phase; 6-Reboiler of alcohol recovery tower.

[0026] 7-Top reflux; 8-Return from reactor bottom; 9-Alcohol recovery tower

[0027] 10, 13 - Circulation aid; 11 - Lactam monomer solution; 12 - Product separation tower

[0028] 14-Lactam monomer Detailed Implementation

[0029] The specific embodiments of the present invention are described in detail below.

[0030] 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%.

[0031] In this application, all pressures mentioned are gauge pressures.

[0032] The continuous production method for lactam monomers provided by this invention refers to an amino acid molecule containing multiple amino or carboxyl groups, wherein the intramolecular dehydration cyclization refers to a reaction involving the amino and carboxyl groups within the amino acid molecule; the amino acid molecule is preferably lysine, selected from one or more of lysine, lysine salts, and aqueous solutions of lysine obtained through bio-fermentation. Its molecular structural formula is as follows:

[0033]

[0034] Lysine feedstock enters the reactor in the form of an aqueous solution, wherein the mass fraction of lysine is 1% to 60%.

[0035] It should be noted that this method also applies to other amino acids containing multiple amino or carboxyl groups, such as glutamic acid and other amino acid molecules with similar structures.

[0036]

[0037] In this invention, the low-carbon alcohols are C1-C4 fatty alcohols, including but not limited to methanol, ethanol, propanol, sec-butanol, tert-butanol, which have boiling points lower than water, as well as n-butanol and isobutanol, which have boiling points higher than water but can form low-boiling-point azeotropes with water.

[0038] The molar ratio of lower alcohols to amino acids is (2-80):1, preferably (5-60):1, and more preferably (10-40):1. Herein, the molar ratio refers to the ratio of the amounts of the two substances.

[0039] In this invention, the reaction temperature of the tower reactor is 140–300°C, more preferably 150–250°C; the pressure at the top of the tower is related to the lower alcohols in the reaction system and also to the reaction temperature, and is the bubble point pressure of the reaction system at 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 section temperature of 150°C, the bubble point pressure of the low-boiling-point azeotrope formed by isobutanol and water is 0.59 MPa; at a reaction section temperature of 250°C, the bubble point pressure of the low-boiling-point azeotrope formed by isobutanol and water is 5.3 MPa.

[0040] Other reaction conditions include a residence time of 0.5–6.0 h for the amino acid feedstock in the reaction section of the tower reactor, preferably 1.0–4.0 h.

[0041] The continuous production system for lactam monomers provided by this invention includes a tower reactor and an alcohol recovery tower. The tower reactor is provided with a raw material inlet, a low-carbon alcohol inlet, and a bottom material outlet for the dehydration and cyclization reaction of amino acids to generate lactam monomers. The alcohol recovery tower is provided with an inlet, a top material outlet, and a bottom material outlet for the recovery of low-carbon alcohols from the reactants. The bottom material outlet of the tower 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.

[0042] In this invention, the alcohol recovery tower is a single distillation tower or two or more distillation towers connected in series. Each distillation tower has an inlet, a top material outlet, and a bottom material outlet. When a low-boiling-point alcohol that does not azeotropically react with water, such as methanol, is used as an additive, a single distillation tower is employed. Methanol is collected at the top material outlet and recycled, while the bottom material is an aqueous solution of lactam monomers. For an alcohol-water azeotropic system, when the water content in the feed is high, the top material is an azeotrope of lower-carbon alcohol and water, and the bottom material outlet is an aqueous solution of lactam monomers. When the water content in the feed is low, the top material is an azeotrope of lower-carbon alcohol and water, and the bottom material outlet is an alcohol solution of lactam monomers.

[0043] In this invention, a reboiler is provided at the bottom of the tower reactor to provide a heat source, and the generated vapor undergoes mass and heat transfer with the liquid phase flowing from bottom to top. In a preferred embodiment, the vapor phase collected from the top of the tower reactor is used as a heat source for the reboiler at the bottom of the alcohol recovery tower. After further heat exchange, it is condensed into a liquid phase and returned to the top of the high-pressure tower reactor in a total reflux manner. An aqueous solution or an alcohol solution rich in lactam monomers is collected from the bottom of the tower, and then sent to a subsequent product separation unit for the separation and purification of lactam monomers. The separated water is discharged, and the separated alcohol is recycled.

[0044] The tower reactor has multiple inlets at the top, from top to bottom: a top reflux inlet, a low-carbon alcohol inlet, an amino acid feed inlet, or a mixture of low-carbon alcohol and amino acid feed introduced through the same inlet. A mixture containing water, low-carbon alcohol, and lactam monomer is collected from the bottom of the tower reactor. This mixture enters an alcohol recovery tower for lactam monomer product and alcohol separation. The bottom of the alcohol recovery tower collects an aqueous solution or an alcohol solution of lactam monomer, while the top collects low-carbon alcohol or an alcohol-water azeotrope. This low-carbon alcohol or alcohol-water azeotrope is recycled back to the tower reactor. The alcohol recovery tower operates at a pressure of -0.08 to 0.5 MPa, a bottom temperature of 60 to 160°C, and a reflux ratio of 0.5 to 3.0.

[0045] The aforementioned tower reactor can be a packed tower or a plate tower, preferably a plate tower. The plate type is selected from conventional forms such as bubble cap plates, valve plates, sieve plates, tongue-shaped plates, and perforated plates. The tower reactor bottom is equipped with a reboiler, with heat supplied by an external heat source. The generated vapor undergoes mass and heat transfer with the liquid phase flowing downwards from bottom to top. The aforementioned alcohol recovery tower can be a packed tower or a plate tower, equipped with a top condenser and a bottom reboiler.

[0046] The above-described apparatus is used for a one-step preparation of lactam monomers from amino acids. The reaction section employs a tower reactor, with a reaction temperature of 140–300°C, more preferably 150–250°C; the top pressure of the tower is the bubble point pressure at the low boiling point or low azeotropic point of the system at the reaction temperature; the residence time of amino acid molecules in the high-temperature reaction zone is 0.5–6.0 h, preferably 1.0–4.0 h. The alcohol recovery tower operates at a pressure of -0.08–0.5 MPa, a bottom temperature of 60–160°C, and a reflux ratio of 0.5–3.0.

[0047] In this invention, the operating pressure of the tower reactor is related to the low-carbon alcohol system used and the reaction temperature. Typically, when methanol is used, the bubble point pressure of the reaction system is 1.3–4.0 MPa, and when isobutanol, which can form a low-boiling-point azeotrope with water, is used, the bubble point pressure of the reaction system is 0.59–5.3 MPa. Therefore, the preferred operating pressure of the tower reactor is between 0.5 and 6.0 MPa.

[0048] The following describes a specific embodiment of the present invention in detail with reference to the accompanying drawings, using the one-step production of aminocaprolactam from lysine with methanol as an adjuvant. 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.

[0049] Appendix Figure 1 A schematic flow chart of one embodiment of a continuous production method for lactam monomers is shown in the attached diagram. Figure 1As shown, a certain concentration of lysine aqueous solution 1 is mixed with recycled methanol 10 in a certain proportion and preheated by heat exchanger 2. After reaching a certain temperature, it is used as reactor feed 3 and enters from the top of tower reactor 4. Due to its high boiling point, lysine flows from top to bottom and is heated to a high temperature by the rising steam in the tower, undergoing an intramolecular dehydration reaction to produce aminocaprolactam. The vapor phase 5 collected from the top of tower reactor 4 is used as the heat source for the reboiler 6 of the subsequent alcohol recovery tower 9, realizing the recovery of latent heat of vapor phase. The remaining heat is recovered by combining with reactor feed 3, becoming a completely liquid phase, and then returned to the top of tower reactor as top reflux 7. The mixture containing methanol, water, and aminocaprolactam collected from the bottom of tower reactor 4 enters alcohol recovery tower 9, recycled methanol 10 is collected from the top of the tower, and aminocaprolactam aqueous solution 11 is collected from the bottom of the tower and sent to the subsequent separation system for further separation and purification of the product.

[0050] The present invention will be further illustrated by the following examples. However, the present invention is not limited thereto.

[0051] 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 isobutanol were commercially available products.

[0052] The contents of lysine and aminocaprolactam in the material were analyzed by external standard method of liquid chromatography.

[0053] The reaction conversion rate X and selectivity S are calculated by the following formula:

[0054]

[0055]

[0056] In the formula: w represents the mass fraction, LYS and N-CPL represent lysine and aminocaprolactam, respectively, and in and out represent reactor inlet and outlet, respectively.

[0057] Comparative Example 1

[0058] Comparative Example 1 uses a conventional tubular reactor to dehydrate lysine to prepare aminocaprolactam. Lysine aqueous solution and methanol enter the tubular reactor from the bottom and are mixed and reacted inside the tubular reactor. The reacted material exits the reactor from the top.

[0059] Lysine aqueous solution is the raw material product of the bio-fermentation process, in which the mass fraction of lysine is 60 wt%, and the remainder is water. The molar ratio of methanol to lysine in the reaction feed is 30:1. The tubular reactor reaction temperature is 180℃, the reaction pressure is 3.6 MPa, and the apparent residence time of the reactants is 2 h.

[0060] The contents of lysine and aminocaprolactam in the raw materials and reactants were analyzed, and the results of reaction selectivity and conversion rate calculations are shown in Table 1. Methanol was recovered from the reactants using a packed column. The operating conditions and reboiler heating amounts of the methanol recovery column are shown in Tables 2 and 3.

[0061] Examples 1-3 illustrate the effects of the continuous production method for lactam monomers of the present invention.

[0062] Example 1

[0063] The reaction process is attached. Figure 1 Lysine aqueous solution and methanol enter the packed tower reactor from the top. Under distillation conditions, the amino acid undergoes dehydration and cyclization to generate lactam monomers. The top material is cooled and completely refluxed, while the bottom material enters the alcohol recovery tower. The methanol separated in the alcohol recovery tower is returned to the tower reactor for recycling, and the remaining material is further separated to obtain lactam monomers. The lysine aqueous solution contains 60 wt% lysine, and the molar ratio of methanol to lysine in the reaction feed is 20:1. The operating conditions of the tower reactor are shown in Table 2. The apparent residence time of the reactants in the tower reactor is 2 hours, and the reaction results are shown in Table 1. The operating conditions of the alcohol recovery tower are the same as those in Table 2. The system has no heat integration, and the energy consumption results are shown in Table 3.

[0064] Example 2

[0065] The reaction process and raw materials used in Example 2 are the same as in Example 1, the difference being the integrated heat system, where the vapor phase collected from the top of the tower reactor is used as the heat source for the bottom of the alcohol recovery tower. The reaction results are shown in Table 1, the tower operating conditions in Table 2, and the energy consumption results in Table 3.

[0066] Example 3

[0067] The reaction process is attached. Figure 2 Lysine aqueous solution and isobutanol enter the packed tower reactor from the top. Under distillation conditions, the amino acid undergoes dehydration and cyclization to generate lactam monomers. The top material is cooled and completely refluxed. The bottom discharge of the tower reactor enters the alcohol recovery tower, which consists of two distillation towers connected in series. The top of alcohol recovery tower 9 collects the azeotrope of isobutanol and water, while the bottom discharge enters product separation tower 12. The top of product separation tower 12 collects isobutanol, and the bottom of product separation tower collects lactam monomer 14. The top materials of both the alcohol recovery tower and the product recovery tower are returned to the tower reactor for recycling. The lysine aqueous solution contains 60 wt% lysine, and the molar ratio of isobutanol to lysine in the reaction feed is 20:1. The operating conditions of the tower reactor and alcohol recovery tower are shown in Table 2. The apparent residence time of the reactants in the tower reactor is 2.5 hours. The reaction results are shown in Table 1.

[0068] Table 1 Reaction Results

[0069]

[0070] Table 2 Operating conditions of tower reactor and alcohol recovery unit

[0071]

[0072] Table 3 Energy Consumption Comparison

[0073]

[0074] The data in Table 1 show that the yields of aminocaprolactam in the comparative example and the embodiment were 70.8% and 81.8%, respectively. The use of a high-pressure tower reactor can significantly improve the product yield.

[0075] The data in Table 3 show that the overall energy consumption of the conventional tubular reactor and methanol recovery tower process is 22.71 MJ / kg product. The energy consumption of the high-pressure tower reactor and low-pressure methanol recovery tower process without thermal integration is 22.18 MJ / kg product, which is basically the same as the conventional process. After thermal integration, the energy consumption is reduced to 18.24 MJ / kg product, which is 19.7% more energy-efficient than the conventional process.

Claims

1. A continuous production method for lactam monomers, characterized in that, The raw material containing amino acids and low-carbon alcohols are fed into a tower reactor. Under distillation conditions, the amino acids are dehydrated and cyclized to generate lactam monomers. The material discharged from the bottom of the tower reactor enters an alcohol recovery tower. The low-carbon alcohols separated in the alcohol recovery tower are returned to the tower reactor for recycling. The remaining materials are further separated to obtain lactam monomers. The low-carbon alcohols have a lower boiling point than water or can form low-boiling-point azeotropes with water. The reaction temperature of the tower reactor is 140–300℃, and the pressure at the top of the tower is the bubble point pressure of the low-boiling-point substances or low azeotropic substances in the system at the actual reaction temperature; the residence time of the raw materials containing amino acids in the tower reactor is 0.5–6.0 h. The amino acid is lysine, and the lower alcohol is selected from one or more of methanol, ethanol, propanol, and butanol. The tower reactor is a packed tower or a plate tower. From top to bottom, the tower reactor has a top reflux port, a low-carbon alcohol inlet, and an amino acid feed inlet, or the low-carbon alcohol and amino acid feed are mixed and added from the same inlet.

2. The continuous production method of lactam monomer according to claim 1, characterized in that, The raw material containing amino acids is selected from one or more of lysine, lysine salts, and aqueous solutions of lysine.

3. The continuous production method of lactam monomer according to claim 2, characterized in that, The raw material containing amino acids is a 1wt% to 60wt% aqueous solution of lysine.

4. The continuous production method of lactam monomer according to claim 1, characterized in that, In the feed to the tower reactor, the molar ratio of the low-carbon alcohol to the amino acid is (2-80):

1.

5. The continuous production method of lactam monomer according to claim 4, characterized in that, In the feed to the tower reactor, the molar ratio of the low-carbon alcohol to the amino acid is (5-60):

1.

6. The continuous production method of lactam monomer according to claim 5, characterized in that, In the feed to the tower reactor, the molar ratio of the low-carbon alcohol to the amino acid is (10-40):

1.

7. A continuous production method for a lactam monomer according to any one of claims 1-6, characterized in that, Inside the tower reactor, the reaction temperature is 150–250°C; the residence time of the amino acid-containing raw material in the tower reactor is 1.0–4.0 h.

8. A continuous production method for a lactam monomer according to any one of claims 1-6, characterized in that, The alcohol recovery tower is constructed using one or more distillation towers connected in series. The operating conditions are: operating pressure of -0.08 to 0.5 MPa, bottom temperature of 60 to 160°C, and reflux ratio of 0.5 to 3.

0.

9. The continuous production method of lactam monomer according to claim 8, characterized in that, The vapor phase collected from the top of the tower reactor is used as the heat source for the reboiler in the alcohol recovery tower. After further heat exchange, it is condensed into a liquid phase and then returned to the top of the tower reactor in a total reflux manner.

10. A continuous production method for a lactam monomer according to any one of claims 1-6, characterized in that, The low-boiling-point alcohols or alcohol-water azeotropes collected from the alcohol recovery tower are returned to the tower reactor.

11. A continuous production apparatus for lactam monomers, characterized in that, A continuous production method for lactam monomers according to any one of claims 1-10 includes a tower reactor and an alcohol recovery tower. The tower reactor is provided with a raw material inlet, a low-carbon alcohol inlet, and a bottom material outlet for an amino acid dehydration cyclization reaction to generate lactam monomers. The alcohol recovery tower is provided with an inlet, a top material outlet, and a bottom material outlet for recovering low-carbon alcohols from the reactants. The bottom material outlet of the tower 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.

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