Method for synthesizing 6-aminocapronitrile from caprolactam

Abstract

The invention provides a method for synthesizing 6-aminocapronitrile from caprolactam. The method comprises the following steps: a gasification device is sequentially provided with a uniform distribution part, an efficient dispersion part, a high-temperature gasification part and an in-situ separation part from top to bottom; liquid-phase caprolactam is injected from the top end of the gasification device, and ammonia gas is injected through the efficient dispersion part; in the efficient dispersion part, liquid-phase caprolactam is broken in a first circular tube nest under the shearing action of gravity and ammonia gas to form liquid drops, and after high-temperature gasification, a gas phase is output from the side part of the gasification device, then enters the reactor filled with the monolithic catalyst from the bottom of the reactor, reacts through the monolithic catalyst and is output from the top of the reactor. According to the invention, caprolactam can be efficiently gasified, coking is not easy to generate, the retention time of a gas-phase reactant in the reactor can be accurately controlled, the reaction efficiency is greatly improved, the discharge amount of wastes in the production process of hexamethylenediamine is reduced, the cost is reduced, the economic benefit is improved, and a guarantee is provided for green, environment-friendly and safe production.

Description

Technical Field

[0001] This invention relates to the field of organic chemical technology, specifically to a method for synthesizing 6-aminohexanonitrile by vaporization and ammonolysis of caprolactam, which is applicable to the efficient preparation of hexamethylenediamine intermediates. Background Technology

[0002] 1,6-Hexamethylenediamine, also known as 1,6-diaminohexane or hexamethylenediamine, is an organic compound with the chemical formula C6H16N2. Hexamethylenediamine is primarily used in the synthesis of nylon 66 and 610 resins, and also in the synthesis of polyurethane resins, ion exchange resins, and hexylene diisocyanates. It is used as a curing agent and organic crosslinking agent for urea-formaldehyde resins and epoxy resins, as well as a stabilizer and bleaching agent in the textile and paper industries, a corrosion inhibitor for aluminum alloys, and an emulsifier for chloroprene rubber. Hexamethylenediamine reacts with hydrochloric acid below 28°C to form 1,6-hexamethylenediamine hydrochloride (6055-52-3), which can be used to produce the bactericide chlorhexidine acetate. Hexamethylenediamine also has some applications in the production of adhesives, aerospace coatings, and rubber vulcanization accelerators. Currently, there are many industrial methods for producing hexamethylenediamine, including the adipic acid method, butadiene method, acrylonitrile method, hexanediol method, and caprolactam method, depending on the raw materials used. Among the methods for producing hexamethylenediamine, the adipic acid method, the butadiene method, and the acrylonitrile dimerization method involve hydrogenating the intermediate adiponitrile to produce hexamethylenediamine. Currently, almost all large-scale hexamethylenediamine production methods utilize the adiponitrile catalytic hydrogenation method. In recent years, with the rapid growth in caprolactam production capacity, the method of synthesizing hexamethylenediamine from caprolactam has received increasing attention. This method generally involves two reaction steps to obtain hexamethylenediamine. The first step is an ammonolysis reaction between caprolactam and ammonia to yield water and 6-aminohexanonitrile. The second step is a reaction between 6-aminohexanonitrile and hydrogen to obtain hexamethylenediamine.

[0003] The bottleneck step in the synthesis of hexamethylenediamine from caprolactam is the ammonolysis reaction of caprolactam, which can be achieved by liquid-phase or gas-phase methods. For example, patent CN107739318A discloses a liquid-phase method for preparing 6-aminohexanonitrile, in which liquid caprolactam and excess hot ammonia are reacted in a gas-liquid two-phase reaction at 260-280°C for approximately 0.5-2 hours, achieving a caprolactam conversion rate of approximately 65%. The problems with the liquid-phase method are low conversion rates and difficulty in catalyst recovery.

[0004] For example, patent CN107602416A discloses a gas-phase method for preparing 6-aminohexanonitrile from caprolactam. The caprolactam is vaporized at high temperature and then reacted with excess hot ammonia at 300-400°C. The reaction time is extremely short (approximately 1 second), requiring strict control, and the conversion rate can reach over 98%. One of the key operations in the gas-phase method is the vaporization of caprolactam. The difficulty in this step lies in the fact that caprolactam is prone to polymerization during high-temperature vaporization, leading to low vaporization efficiency and low selectivity in subsequent reactions. To enhance the vaporization process of caprolactam, hot ammonia, another raw material in the reaction process, is usually used as a heat source to vaporize the caprolactam. Patents CN 112321456 B, CN 115260058 B, CN116603460A, and CN 118987637 A disperse liquid caprolactam using a ring-shaped liquid phase distribution device and then heat and vaporize it with high-temperature ammonia. In this method, the caprolactam distribution device is typically directly exposed to high-temperature ammonia gas. After prolonged use, the outlet of the distribution device often becomes clogged due to caprolactam polymerization, resulting in uneven distribution of liquid caprolactam, leading to poor vaporization and severe polymerization. Patents CN 113426377 A and CN 116617690 A introduce ammonia gas into a venturi tube, creating a negative pressure at the throat. This negative pressure vaporizes the caprolactam, which then enters the venturi tube through a side tube of the throat, merging with the ammonia gas. In this method, the throat is relatively narrow, making it prone to clogging and difficult to maintain stable operation over a long period. Another key operation in the gas-phase method is accurately controlling the residence time of the gas phase in the reactor. This reaction is an extremely rapid chemical reaction, requiring only a few seconds. Currently, most of the reactors used in related patents for this reaction are fluidized bed or fixed bed reactors, which suffer from a wide residence time distribution. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for synthesizing 6-aminohexanonitrile from caprolactam, which can not only efficiently vaporize caprolactam and avoid coking, but also accurately control the residence time of gaseous reactants in the reactor, greatly improve reaction efficiency, reduce the amount of waste generated during the production of hexamethylenediamine, reduce costs, improve economic benefits, and provide a guarantee for green, environmentally friendly and safe production.

[0006] This invention is implemented as follows: A method for synthesizing 6-aminohexanonitrile from caprolactam includes the following steps: (1) Gasification process: Liquid caprolactam is injected from the top of the gasification device, and ammonia is injected through the high-efficiency dispersion component to disperse caprolactam into droplets; the gasification device is arranged from top to bottom as a uniform distribution component, a high-efficiency dispersion component, a high-temperature gasification component and an in-situ separation component; The uniform distribution component includes an elliptical end cap and a bottom plate with circular holes. Each circular hole is connected to a circular tube of the same diameter, and the outlet of the circular tube narrows. The lower end of the circular tube extends into the high-efficiency dispersing component. The high-efficiency dispersing component includes a uniformly distributed first circular tube column, the position and number of which correspond to the uniformly distributed circular tube component. The high-temperature gasification component includes a shell-and-tube heat exchanger, with the heated fluid flowing through the tube side and the heat transfer fluid flowing through the shell side; a second circular tube is evenly distributed in the middle of the shell-and-tube heat exchanger, and the second circular tube is connected to the first circular tube in a one-to-one correspondence and is integrally formed. The in-situ separation component is located at the bottom of the gasification device and is used to separate unvaporized caprolactam; Within the high-efficiency dispersion component, the liquid phase caprolactam breaks into droplets in the first circular tube under the shearing action of gravity and ammonia. After being vaporized at high temperature, the gas phase is output from the side of the vaporization device, while the unvaporized liquid phase is discharged from the bottom. (2) Reaction process: The gaseous material enters from the bottom of the reactor filled with the monolithic catalyst, reacts with the monolithic catalyst, and is output from the top.

[0007] Furthermore, the diameter of the constriction outlet of the circular tube is reduced by 20% compared to the diameter of the circular tube; The diameter and length of the circular tubes of the uniformly distributed component range from 1-3 mm and 1-20 cm, respectively, and the length of the contraction outlet ranges from 1-2 cm; the circular tubes are distributed in a ring on the disc, and the distance between the tubes ranges from 3-6 mm.

[0008] Furthermore, the diameter of the first circular tube of the high-efficiency dispersing component is 20% larger than the diameter of the circular tube of the uniform distribution component; the length of the first circular tube is 1-20cm.

[0009] Furthermore, the length of the second circular tube within the high-temperature gasification component ranges from 100 to 300 cm.

[0010] Furthermore, in step (1), the feed temperature range of liquid caprolactam and ammonia is 50-150℃, and the molar ratio of the two materials is ammonia:caprolactam = 5-50:1.

[0011] Furthermore, the outlet material temperature range of the high-temperature gasification component in step (1) is 300-450℃.

[0012] Furthermore, the operating pressure range of the gasification device in step (1) is 1-200 kPa.

[0013] Furthermore, in step (2), the integral structure catalyst has a honeycomb structure, with the honeycomb channel near the center having a smaller hydraulic diameter and the channel far from the center having a larger hydraulic diameter.

[0014] Furthermore, the cross-section of the integral catalyst flow channel described in step (2) is circular, with a hydraulic diameter ranging from 5 to 30 mm; it is based on cordierite honeycomb ceramic and coated with an acidic or alkaline catalyst coating.

[0015] Furthermore, the reaction device described in step (2) adopts two sets of parallel integrated catalyst devices, one for use and one for standby.

[0016] The present invention has the following advantages: The dispersion and vaporization of liquid caprolactam in this invention are carried out separately, which can avoid the influence of polymer coking generated during the high-temperature vaporization process on the liquid caprolactam dispersion device. In step (1), caprolactam is broken into small droplets in the microchannel of the sleeve flow focusing structure at a lower temperature by the driving force of liquid phase gravity and ammonia shear force. The process of forming small droplets in this structure is stable, the resulting droplets are uniform in size, and the droplets in different channels do not affect each other, which is extremely beneficial for subsequent vaporization. The vaporization of droplets is carried out in the microtube of the high-temperature vaporization component. The droplets do not directly contact the tube wall, but are separated by hot ammonia. The heat transfer agent transfers heat to ammonia through indirect convection heat transfer, and ammonia then transfers heat to caprolactam through direct contact convection heat transfer. This can effectively avoid overheating and coking of caprolactam.

[0017] In addition, the present invention uses an integral catalyst for the gas-phase reaction of caprolactam and ammonia, and the channels of the integral catalyst are honeycomb structure. The honeycomb channels near the center have a smaller hydraulic diameter, while the channels far from the center have a larger hydraulic diameter, which can improve the uniformity of flow distribution and enhance the scale-up capability of the equipment.

[0018] In summary, this invention employs a four-component integrated gasification device (uniform distribution → dispersion → gasification → separation) to achieve efficient gasification of caprolactam. Combined with a variable-diameter honeycomb integral catalyst reactor, it solves the problems of gasification coking and reaction residence time distribution, greatly improving the gasification rate and conversion rate of the reaction. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 The present invention relates to the structure of a gasification apparatus and a reaction apparatus for a method of synthesizing 6-aminohexanonitrile from caprolactam.

[0021] Figure 2 for Figure 1 Cross-sectional view along the AA direction.

[0022] The attached figures are numbered as follows: 100 - Gasification device; 200 - Reaction device; 1-Liquid phase caprolactam inlet, 2-Uniform distribution component, 21-Elliptical end cap; 22-Bottom plate, 23-Circular tube, 3-High-efficiency dispersion component, 31-First circular tube, 32-Ammonia inlet, 4-High-temperature gasification component, 41-Second circular tube, 42-Heat transfer agent inlet, 43-Heat transfer agent outlet; 5-In-situ separation component, 6-Gas phase material outlet, 7-Valve, 8-Reactor inlet, 9-Integral catalyst, 91-Honeycomb channel, 10-Reactor outlet. Detailed Implementation

[0023] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] See Figure 1-2 Liquid caprolactam is injected from the liquid caprolactam inlet 1 at the top of the gasification device 100, and after being distributed by the uniform distribution component 2, it enters the high-efficiency dispersion component 3. At the same time, ammonia gas is injected through the ammonia gas inlet 32 ​​on the side of the high-efficiency dispersion component 3, which directly contacts the liquid caprolactam and disperses it into small droplets. The caprolactam and ammonia gas dispersed into small droplets enter the high-temperature gasification component 4 together, where they are heated and the liquid caprolactam is vaporized. The unvaporized caprolactam leaves from the in-situ separation component 5 at the bottom of the gasification device 100 under the action of gravity, and the gas phase leaves from the gas phase material outlet 6 on the side of the gasification device 100 and enters from the reactor inlet 8 below the reaction device 200. After being reacted by the integral catalyst 9, it is output from the top reactor outlet 10.

[0026] The following will be combined with the appendix Figure 1-2The technical solution of the present invention will be clearly and completely described in detail with specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. Example 1

[0027] The operating pressure of the gasification unit is 10 kPa. The feed temperatures of liquid caprolactam and ammonia are both 100°C, and the feed molar ratio is 20:1 (ammonia:caprolactam). The inlet temperature of the heat transfer agent is 400°C. The outlet flow velocity of the uniform distribution component for liquid caprolactam is 0.5 m / s, the diameter of the outlet circular tube is 1 mm, the length is 15 cm, and the tube spacing is 4 mm. The length of the second circular tube of the high-temperature gasification component for liquid caprolactam is 200 cm, and the outlet gas phase temperature is 380°C. The monolithic catalyst is coated with an alkaline catalyst coating, and the honeycomb channel has a hydraulic diameter that increases uniformly and monotonously from 5 mm to 30 mm from the center to the periphery. The gasification rate of the gasification unit is 95%, and the conversion rate and selectivity of the reaction unit are 97% and 99.5%, respectively. The specific calculation method is as follows: ; ; Wherein, the mass of caprolactam at the reactor inlet = the mass of caprolactam in the liquid phase at the gasification unit inlet - the mass of caprolactam not gasified in the gasification unit; . Example 2

[0028] The operating pressure of the gasification unit is 10 kPa. The feed temperature of both liquid caprolactam and ammonia is 150℃, and the feed molar ratio is 20:1 (ammonia:caprolactam). The inlet temperature of the heat transfer agent is 400℃. The outlet flow rate of the uniform distribution component for liquid caprolactam is 0.5 m / s. The diameter of the outlet circular tube is 1 mm, the length is 15 cm, and the tube spacing is 4 mm. The high-temperature gasification component for liquid caprolactam has a tube length of 200 cm and an outlet gas phase temperature of 380℃. The monolithic catalyst is coated with an alkaline catalyst coating, and the honeycomb channel has a hydraulic diameter that increases uniformly and monotonously from 5 mm to 30 mm from the center to the periphery. The gasification rate of the gasification unit is 97%, and the conversion rate and selectivity of the reaction unit are 97% and 99.5%, respectively. Example 3

[0029] The operating pressure of the gasification unit is 20 kPa. The feed temperature of both liquid caprolactam and ammonia is 100℃, and the feed molar ratio is 20:1 (ammonia:caprolactam). The inlet temperature of the heat transfer agent is 400℃. The outlet flow rate of the uniform distribution component for liquid caprolactam is 0.5 m / s. The diameter of the outlet circular tube is 1 mm, the length is 15 cm, and the tube spacing is 4 mm. The high-temperature gasification component for liquid caprolactam has a tube length of 200 cm and an outlet gas phase temperature of 380℃. The monolithic catalyst is coated with an alkaline catalyst coating, and the honeycomb channel has a hydraulic diameter that increases uniformly and monotonously from 5 mm to 30 mm from the center to the periphery. The gasification rate of the gasification unit is 91%, and the conversion rate and selectivity of the reaction unit are 97% and 99.5%, respectively. Example 4

[0030] The operating pressure of the gasification unit is 10 kPa. The feed temperature of both liquid caprolactam and ammonia is 100℃, and the feed molar ratio is 30:1 (ammonia:caprolactam). The inlet temperature of the heat transfer agent is 400℃. The outlet flow rate of the uniform distribution component for liquid caprolactam is 0.5 m / s. The diameter of the outlet circular tube is 1 mm, the length is 15 cm, and the tube spacing is 4 mm. The high-temperature gasification component for liquid caprolactam has a tube length of 200 cm and an outlet gas phase temperature of 380℃. The monolithic catalyst is coated with an alkaline catalyst coating, and the honeycomb channel has a hydraulic diameter that increases uniformly and monotonously from 5 mm to 30 mm from the center to the periphery. The gasification rate of the gasification unit is 97%, and the conversion rate and selectivity of the reaction unit are 99% and 99.5%, respectively. Example 5

[0031] The operating pressure of the gasification unit is 10 kPa. The feed temperature of both liquid caprolactam and ammonia is 100℃, and the feed molar ratio is 20:1 (ammonia:caprolactam). The inlet temperature of the heat transfer agent is 350℃. The outlet flow rate of the uniform distribution component for liquid caprolactam is 0.5 m / s. The diameter of the outlet circular tube is 1 mm, the length is 15 cm, and the tube spacing is 4 mm. The high-temperature gasification component for liquid caprolactam has a tube length of 200 cm and an outlet gas phase temperature of 300℃. The monolithic catalyst is coated with an alkaline catalyst coating, and the honeycomb channel has a hydraulic diameter that increases uniformly and monotonously from 5 mm to 30 mm from the center to the periphery. The gasification rate of the gasification unit is 90%, and the conversion rate and selectivity of the reaction unit are 94% and 99.8%, respectively.

[0032] In summary, the dispersion and vaporization of liquid caprolactam in this invention are carried out separately, which avoids the influence of polymer coking generated during the high-temperature vaporization process on the liquid caprolactam dispersion device. In step (1), caprolactam is broken into small droplets in the microchannel of the sleeve flow focusing structure at a lower temperature by the driving force of liquid phase gravity and ammonia shear force. The process of forming small droplets in this structure is stable, the resulting droplets are uniform in size, and the droplets in different channels do not affect each other, which is extremely beneficial for subsequent vaporization. The vaporization of droplets is carried out in the microtube of the high-temperature vaporization component. The droplets do not directly contact the tube wall, but are separated by hot ammonia. The heat transfer agent transfers heat to the ammonia through indirect convection heat transfer, and the ammonia then transfers heat to the caprolactam through direct contact convection heat transfer. This can effectively avoid overheating and coking of caprolactam.

[0033] In addition, the present invention uses an integral catalyst for the gas-phase reaction of caprolactam and ammonia, and the channels of the integral catalyst are honeycomb structure. The honeycomb channels near the center have a smaller hydraulic diameter, while the channels far from the center have a larger hydraulic diameter, which can improve the uniformity of flow distribution and enhance the scale-up capability of the equipment.

[0034] In summary, this invention employs a four-component integrated gasification device (uniform distribution → dispersion → gasification → separation) to achieve efficient gasification of caprolactam. Combined with a variable-diameter honeycomb integral catalyst reactor, it solves the problems of gasification coking and reaction residence time distribution, greatly improving the gasification rate and conversion rate of the reaction.

[0035] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for synthesizing 6-aminohexanonitrile from caprolactam, characterized in that: Includes the following steps: (1) Gasification process: Liquid caprolactam is injected from the top of the gasification device, and ammonia is injected through the high-efficiency dispersion component to disperse caprolactam into droplets; the gasification device is arranged from top to bottom as a uniform distribution component, a high-efficiency dispersion component, a high-temperature gasification component and an in-situ separation component; The uniform distribution component includes an elliptical end cap and a bottom plate with circular holes. Each circular hole is connected to a circular tube of the same diameter, and the outlet of the circular tube narrows. The lower end of the circular tube extends into the high-efficiency dispersing component. The high-efficiency dispersing component includes a uniformly distributed first circular tube, the position and number of which correspond to the uniformly distributed circular tubes; The high-temperature gasification component includes a shell-and-tube heat exchanger, with the heated fluid flowing through the tube side and the heat transfer fluid flowing through the shell side; a second circular tube is evenly distributed in the middle of the shell-and-tube heat exchanger, and the second circular tube is connected to the first circular tube in a one-to-one correspondence and is integrally formed. The in-situ separation component is located at the bottom of the gasification device and is used to separate unvaporized caprolactam; Within the high-efficiency dispersion component, the liquid phase caprolactam breaks into droplets in the first circular tube under the shearing action of gravity and ammonia. After being vaporized at high temperature, the gas phase is output from the side of the vaporization device, while the unvaporized liquid phase is discharged from the bottom. (2) Reaction process: The gaseous material enters from the bottom of the reactor filled with the monolithic catalyst, reacts with the monolithic catalyst, and is output from the top.

2. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The diameter of the constricted outlet of the circular tube is 20% smaller than the diameter of the circular tube. The diameter and length of the circular tubes of the uniformly distributed component range from 1-3 mm and 1-20 cm, respectively, and the length of the contraction outlet ranges from 1-2 cm; the circular tubes are distributed in a ring on the disc, and the distance between the tubes ranges from 3-6 mm.

3. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The diameter of the first circular tube of the high-efficiency dispersing component is 20% larger than the diameter of the circular tube of the uniform distribution component; the length of the first circular tube is 1-20cm.

4. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The length of the second circular tube within the high-temperature gasification component ranges from 100 to 300 cm.

5. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The feed temperature range of liquid caprolactam and ammonia in step (1) is 50-150℃, and the molar ratio of the two materials is ammonia:caprolactam = 5-50:

1.

6. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The outlet material temperature range of the high-temperature gasification component in step (1) is 300-450℃.

7. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The operating pressure range of the gasification device in step (1) is 1-200 kPa.

8. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: In step (2), the integral structure catalyst has a honeycomb structure, with the honeycomb channel near the center having a smaller hydraulic diameter and the channel far from the center having a larger hydraulic diameter.

9. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 8, characterized in that: The integral catalyst flow channel described in step (2) has a circular cross-section with a hydraulic diameter ranging from 5 to 30 mm; it is based on cordierite honeycomb ceramic and coated with an acidic or alkaline catalyst coating.

10. The method for synthesizing 6-aminohexanonitrile from caprolactam according to claim 1, characterized in that: The reaction device described in step (2) uses two sets of parallel integrated catalyst devices, one for use and one for standby.

Images