A device and method for gradient hydrolysis of waste polyamide 6

Abstract

The present invention belongs to the technical field of waste material recovery and reuse, and relates to a device and method for gradient hydrolysis of waste polyamide 6. The device mainly comprises a cylinder and a multi-layer hydrolysis tower plate, and the hydrolysis tower plates are arranged in a cylinder from top to bottom; the hydrolysis tower plate is a conical plate, and a superheated water vapor through hole is provided on it; a set of drainage devices is provided between two adjacent hydrolysis tower plates; a superheated water vapor through hole and a melt inlet are provided on the top of the cylinder, and a superheated water vapor through hole is provided on the bottom. Method: Superheated water vapor is transported into the cylinder from the superheated water vapor through hole at the bottom of the cylinder, and waste polyamide 6 melt is transported into the cylinder from the melt inlet at the same time, and the melt in the melt storage cavity surrounded by each hydrolysis tower plate and the cylinder is collected, so as to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees. The present invention adopts a gradient hydrolysis method to depolymerize waste polyamide 6 macromolecules into products with different hydrolysis degrees, thereby improving the comprehensiveness, diversity and flexibility of recycling.

Description

Technical Field

[0001] The invention belongs to the technical field of waste material recovery and reuse, and relates to a device and method for gradient hydrolyzing waste polyamide 6. Background Art

[0002] Polyamide 6, also known as nylon 6, is a high-toughness and high-strength polyamide product made by hydrolysis and polymerization of caprolactam, which is widely used in the fields of plastics and fibers. Although its stable chemical properties bring good application effects, it also leads to the problem of difficult degradation after disposal. At present, the main way to deal with waste polyamide 6 is still landfill or incineration, which can not be ignored. The damage to the ecological environment and the economic losses caused by this cannot be ignored. Therefore, it has become an inevitable trend to recycle waste polyamide 6 to achieve recycling or extend its service life.

[0003] Chemical recycling methods, especially hydrolysis methods, have higher recycling efficiency and wider application potential than physical recycling methods because they can depolymerize waste polyamide 6 macromolecules into monomers, oligomers or corresponding derivatives. However, the current research and application of hydrolysis methods are mostly focused on the recovery of a single target product (caprolactam), such as a polyamide 6 efficient catalytic hydrolysis and reuse method disclosed in patent application CN202311763812.7. This approach ignores the multi-level energy and value contained in the initial polymerization process of waste polyamide 6, limiting its comprehensiveness in recycling.

[0004] In addition, based on the traditional way of recycling to monomers, the existing hydrolysis-based polyamide 6 recovery devices are mostly designed around concentrating and purifying the hydrolyzate (caprolactam aqueous solution), such as the four-effect concentration device described in patent application CN103495285B, which aims to concentrate and purify the extracted water into a reusable caprolactam concentrate. However, for the demand for recycling low-molecular polyamide 6 with different polymerization degrees, there is currently a lack of specialized recovery devices and technical solutions on the market, which limits the diversity and flexibility of recycling waste polyamide 6. Summary of the invention

[0005] The purpose of the present invention is to solve the problems existing in the prior art and to provide a device and method for gradient hydrolysis of waste polyamide 6.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A device for gradient hydrolysis of waste polyamide 6, comprising a cylinder and n hydrolysis trays arranged in the cylinder from top to bottom (used to guide the waste polyamide 6 melt to flow downward and increase the contact area with water vapor, and a hydrolysis reaction occurs in the process), n≥2;

[0008] The hydrolysis tower plate is provided with a superheated water vapor through hole, the aperture of which is ≥100 meshes. Such aperture setting can ensure the passage of superheated water vapor while preventing the passage of melt;

[0009] The hydrolysis tower plate is a conical plate, the tip of which is the highest point and the edge of which is sealed and connected to the cylinder body, and the hydrolysis tower plate and the cylinder body form a melt storage chamber;

[0010] A drainage device is provided between two adjacent hydrolysis trays, and the drainage device is used to drain the melt in the melt storage cavity surrounded by the hydrolysis tray located above and the cylinder to the outside of the cylinder or the tip of the hydrolysis tray located below; each drainage device includes m evenly distributed three-way valves, m≥4; the inlet of each three-way valve is connected to the melt storage cavity, one outlet is connected to the inlet of a melt outlet pipe located outside the cylinder (used to guide the hydrolyzed waste polyamide 6 melt out of the hydrolysis tower), and the other outlet is connected to the inlet of a melt conveying pipe a located inside the cylinder (used to convey the hydrolyzed waste polyamide 6 melt downward);

[0011] A superheated steam through hole and a melt inlet (used to transport waste polyamide 6 melt into the cylinder) are provided on the top of the cylinder. The melt inlet faces the tip of the uppermost hydrolysis tower plate. A superheated steam through hole is provided at the bottom of the cylinder.

[0012] As the preferred technical solution:

[0013] In the device for gradient hydrolysis of waste polyamide 6 as described above, the distance between two adjacent hydrolysis tower plates is 10-15 cm.

[0014] A device for gradient hydrolysis of waste polyamide 6 as described above, 5≤n≤10.

[0015] In the above-mentioned device for gradient hydrolysis of waste polyamide 6, the distribution density of the superheated water vapor holes on the hydrolysis tower plate is ≥5 / cm 3 .

[0016] In the device for gradient hydrolysis of waste polyamide 6 as described above, the thickness of the hydrolysis tower plate is 10-20 mm, the conical plate is conical, the cone angle is 30-80°, and the height is 30-100 cm.

[0017] In the device for gradient hydrolysis of waste polyamide 6 as described above, all the hydrolysis tower plates are coaxial.

[0018] In the device for gradient hydrolysis of waste polyamide 6 as described above, in the same set of drainage devices, the outlets of all melt conveying pipes a converge into a single outlet, and all melt conveying pipes a form a funnel-shaped structure.

[0019] In the device for gradient hydrolysis of waste polyamide 6 as described above, the melt storage chamber surrounded by the nth hydrolysis tower plate and the cylinder is connected to the inlet of at least one melt delivery pipe b located in the cylinder, and the outlet of the melt delivery pipe b is connected to the outside of the cylinder.

[0020] In the above-mentioned device for gradient hydrolysis of waste polyamide 6, the distribution density of the superheated water vapor holes on the top and bottom of the cylinder is ≥5 / cm 3 The shape of the superheated steam through hole on the top and bottom of the cylinder is a truncated cone, the diameter of the upper bottom of the truncated cone is 1~5mm, the diameter of the lower bottom is 5~10mm, and the upper bottom is located above the lower bottom.

[0021] The device for gradient hydrolysis of waste polyamide 6 as described above has a cylindrical barrel, an operating temperature range of 25-300°C, an upper pressure resistance limit of 10MPa, and an aspect ratio of 3-10.

[0022] The present invention also provides a method for gradient hydrolysis of waste polyamide 6 using a device for gradient hydrolysis of waste polyamide 6 as described in any of the above items, wherein superheated water vapor is transported into the cylinder from the superheated water vapor through hole at the bottom of the cylinder, and at the same time, the waste polyamide 6 melt is transported into the cylinder from the melt inlet, and the melt in the melt storage cavity formed by each hydrolysis tower plate and the cylinder is collected to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees.

[0023] As the preferred technical solution:

[0024] In the above-mentioned method for gradient hydrolysis of waste polyamide 6, the temperature of the superheated water vapor is 220~300°C, the conveying speed is 20~150kg / h, and the input pressure is 0.5~3MPa; the relative viscosity of the waste polyamide 6 melt is 4.0~2.4, the number average molecular weight is 40000~12000g / mol, and the conveying speed is 20~50kg / h.

[0025] Beneficial effects:

[0026] The present invention can depolymerize waste polyamide 6 macromolecules into products with different hydrolysis degrees by means of gradient hydrolysis. Compared with the method of recovering a single target product, it more comprehensively explores the multi-level energy and value in the initial polymerization process of waste polyamide 6, and improves the diversity and flexibility of the recycling of waste polyamide 6. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a cross-sectional schematic diagram of a device for gradient hydrolysis of waste polyamide 6 of the present invention;

[0028] Figure 2 It is a top view schematic diagram of the hydrolysis tower plate of the device for gradient hydrolysis of waste polyamide 6 of the present invention (only m is shown as 4 in the figure);

[0029] Among them, 1-melt inlet, 2-hydrolysis tower plate, 3-superheated water vapor through hole, 4-three-way valve, 5-melt outlet pipe, 6-melt conveying pipe a, 7-melt conveying pipe b. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0031] A device for gradient hydrolysis of waste polyamide 6, such as Figure 1 As shown, it includes a cylinder, a hydrolysis tower plate 2, and a drainage device;

[0032] The number of hydrolysis trays 2 is n, 2≤n≤10, the n hydrolysis trays 2 are located in the cylinder and arranged from top to bottom, the distance between two adjacent hydrolysis trays 2 is 10-15 cm; the hydrolysis tray 2 is a conical tray, the thickness is 10-20 mm, the cone angle is 30-80°, and the height of the cone is 30-100 cm; the tip of the hydrolysis tray 2 is the highest point and the edge is sealed and connected to the cylinder, the hydrolysis tray 2 and the cylinder form a melt storage chamber; all the hydrolysis trays 2 are coaxial; Figure 2 As shown, the hydrolysis tower plate 2 is provided with superheated water vapor through holes 3; the aperture of the superheated water vapor through holes 3 is ≥ 100 mesh, and the distribution density is ≥ 5 / cm 3 ;

[0033] A drainage device is provided between two adjacent hydrolysis trays, and the drainage device is used to drain the melt in the melt storage cavity surrounded by the hydrolysis tray 2 located above and the cylinder to the outside of the cylinder or the tip of the hydrolysis tray located below; Figure 1 , Figure 2 As shown, each set of drainage devices includes m evenly distributed three-way valves 4, m≥4, the inlet of each three-way valve 4 is connected to the melt storage chamber, one outlet is connected to the inlet of a melt outlet pipe 5 located outside the cylinder, and the other outlet is connected to the inlet of a melt delivery pipe a 6 located inside the cylinder; in the same set of drainage devices, the outlets of all melt delivery pipes a 6 converge into a single outlet, and all melt delivery pipes a 6 form a funnel-shaped structure; as shown Figure 1 As shown, the melt storage cavity formed by the nth hydrolysis tray 2 and the cylinder is connected to the inlet of at least one melt delivery pipe b7 located in the cylinder, and the outlet of the melt delivery pipe b7 is connected to the outside of the cylinder;

[0034] The cylinder is cylindrical, with an operating temperature range of 25~300℃, an upper pressure limit of 10MPa, and an aspect ratio of 3~10; Figure 1 As shown, the top of the cylinder is provided with a superheated water vapor through hole and a melt inlet 1, the melt inlet 1 is directly opposite to the tip of the hydrolysis tower plate 2 located at the top, and the bottom of the cylinder is provided with a truncated cone-shaped superheated water vapor through hole; the distribution density of the truncated cone-shaped superheated water vapor through holes on the top and bottom of the cylinder is ≥5 / cm 3 The diameter of the upper base of the truncated cone is 1~5mm, the diameter of the lower base of the truncated cone is 5~10mm, and the upper base is located above the lower base.

[0035] In the following embodiments, hydrolyzate 1 represents the hydrolyzate of waste polyamide 6 collected from the melt storage chamber surrounded by the first hydrolysis tray and the cylinder from top to bottom, hydrolyzate 2 represents the hydrolyzate of waste polyamide 6 collected from the melt storage chamber surrounded by the second hydrolysis tray and the cylinder from top to bottom, hydrolyzate 3 represents the hydrolyzate of waste polyamide 6 collected from the melt storage chamber surrounded by the third hydrolysis tray and the cylinder from top to bottom, hydrolyzate 4 represents the hydrolyzate of waste polyamide 6 collected from the melt storage chamber surrounded by the fourth hydrolysis tray and the cylinder from top to bottom, and hydrolyzate 5 represents the hydrolyzate of waste polyamide 6 collected from the melt storage chamber surrounded by the fifth hydrolysis tray and the cylinder from top to bottom. Products, hydrolysis product 6 represents the hydrolysis product of waste polyamide 6 collected from the melt storage chamber surrounded by the 6th hydrolysis tray and the cylinder from top to bottom, hydrolysis product 7 represents the hydrolysis product of waste polyamide 6 collected from the melt storage chamber surrounded by the 7th hydrolysis tray and the cylinder from top to bottom, hydrolysis product 8 represents the hydrolysis product of waste polyamide 6 collected from the melt storage chamber surrounded by the 8th hydrolysis tray and the cylinder from top to bottom, hydrolysis product 9 represents the hydrolysis product of waste polyamide 6 collected from the melt storage chamber surrounded by the 9th hydrolysis tray and the cylinder from top to bottom, and hydrolysis product 10 represents the hydrolysis product of waste polyamide 6 collected from the melt storage chamber surrounded by the 10th hydrolysis tray and the cylinder from top to bottom;

[0036] t1 represents the time from when the waste polyamide 6 melt is transported from the melt inlet to the cylinder to obtain hydrolyzate 1, t2 represents the time from when the waste polyamide 6 melt is transported from the melt inlet to the cylinder to obtain hydrolyzate 2, and t3 represents the time from when the waste polyamide 6 melt is transported from the melt inlet to the cylinder to obtain hydrolyzate 3.

[0037] Example 1

[0038] A method for gradient hydrolysis of waste polyamide 6, using the device for gradient hydrolysis of waste polyamide 6 as described above, with the following specific steps:

[0039] (1) Preparation of raw materials;

[0040] Waste polyamide 6 melt: relative viscosity is 2.4, number average molecular weight is 12000g / mol;

[0041] (2) Superheated water vapor with a temperature of 220° C. is delivered into the cylinder from the superheated water vapor through hole at the bottom of the cylinder at a delivery rate of 20 kg / h, and waste polyamide 6 melt is delivered into the cylinder from the melt inlet at a delivery rate of 20 kg / h, and the melt in the melt storage cavity surrounded by each hydrolysis tray and the cylinder is collected to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees;

[0042] The size parameters of the device for gradient hydrolysis of waste polyamide 6 are as follows: n is 2, the distance between two adjacent hydrolysis tower plates is 15 cm, the thickness of the hydrolysis tower plate is 20 mm, the cone angle is 30°, the height of the cone is 100 cm, the aperture of the superheated water vapor through hole on the hydrolysis tower plate is 300 mesh, and the distribution density of the superheated water vapor through hole on the hydrolysis tower plate is 5 / cm 3 , m is 4, the number of melt delivery pipes b is 1, the aspect ratio of the cylinder is 3, and the distribution density of the truncated cone-shaped superheated water vapor holes on the top and bottom of the cylinder is 5 / cm 3 The upper base diameter of the truncated cone is 1 mm, and the lower base diameter of the truncated cone is 5 mm.

[0043] The relative viscosity of hydrolyzate 1 is 2, and t1 is 20 min; the relative viscosity of hydrolyzate 2 is 1.8, and t2 is 38 min; if the melt is drained to the outside of the cylinder only at the end, the yield of hydrolyzate 2 is 95%, indicating that most of the waste polyamide 6 melt has been converted into hydrolyzate 2.

[0044] Example 2

[0045] A method for gradient hydrolysis of waste polyamide 6, using the device for gradient hydrolysis of waste polyamide 6 as described above, with the following specific steps:

[0046] (1) Preparation of raw materials;

[0047] Waste polyamide 6 melt: relative viscosity is 3.0, number average molecular weight is 23000g / mol;

[0048] (2) Superheated water vapor with a temperature of 240° C. is transported into the cylinder from the superheated water vapor through hole at the bottom of the cylinder at a transport rate of 60 kg / h, and waste polyamide 6 melt is transported into the cylinder from the melt inlet at a transport rate of 30 kg / h, and the melt in the melt storage cavity surrounded by each hydrolysis tray and the cylinder is collected to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees;

[0049] The size parameters of the device for gradient hydrolysis of waste polyamide 6 are as follows: n is 3, the distance between two adjacent hydrolysis tower plates is 13 cm, the thickness of the hydrolysis tower plate is 18 mm, the cone angle is 45°, the height of the cone is 80 cm, the aperture of the superheated water vapor through hole on the hydrolysis tower plate is 200 mesh, and the distribution density of the superheated water vapor through hole on the hydrolysis tower plate is 10 / cm 3 , m is 6, the number of melt delivery pipes b is 2, the aspect ratio of the cylinder is 5, and the distribution density of the truncated cone-shaped superheated water vapor holes on the top and bottom of the cylinder is 10 / cm 3 The upper base diameter of the truncated cone is 2 mm, and the lower base diameter of the truncated cone is 7 mm.

[0050] The relative viscosity of hydrolyzate 1 is 2.7, and t1 is 24 min; the relative viscosity of hydrolyzate 2 is 2.3, and t2 is 46 min; the relative viscosity of hydrolyzate 3 is 1.8, and t3 is 66 min; if the melt is drained to the outside of the cylinder only at the end, the yield of hydrolyzate 3 is 85%, indicating that most of the waste polyamide 6 melt has been converted into hydrolyzate 3.

[0051] Example 3

[0052] A method for gradient hydrolysis of waste polyamide 6, using the device for gradient hydrolysis of waste polyamide 6 as described above, with the following specific steps:

[0053] (1) Preparation of raw materials;

[0054] Waste polyamide 6 melt: relative viscosity is 3.5, number average molecular weight is 29000g / mol;

[0055] (2) Superheated water vapor with a temperature of 280° C. is transported into the cylinder from the superheated water vapor through hole at the bottom of the cylinder at a transport rate of 100 kg / h, and waste polyamide 6 melt is transported into the cylinder from the melt inlet at a transport rate of 40 kg / h, and the melt in the melt storage cavity surrounded by each hydrolysis tray and the cylinder is collected to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees;

[0056] The size parameters of the device for gradient hydrolysis of waste polyamide 6 are as follows: n is 5, the distance between two adjacent hydrolysis tower plates is 11 cm, the thickness of the hydrolysis tower plate is 14 mm, the cone angle is 60°, the height of the cone is 55 cm, the aperture of the superheated water vapor through hole on the hydrolysis tower plate is 150 mesh, and the distribution density of the superheated water vapor through hole on the hydrolysis tower plate is 15 / cm 3 , m is 8, the number of melt delivery pipes b is 3, the aspect ratio of the cylinder is 7, and the distribution density of the truncated cone-shaped superheated water vapor holes on the top and bottom of the cylinder is 15 / cm 3The upper base diameter of the truncated cone is 3mm, and the lower base diameter of the truncated cone is 9mm.

[0057] The relative viscosity of hydrolysate 1 is 3.1, the relative viscosity of hydrolysate 2 is 2.6, the relative viscosity of hydrolysate 3 is 2, the relative viscosity of hydrolysate 4 is 1.5, and the relative viscosity of hydrolysate 5 is 1.

[0058] Example 4

[0059] A method for gradient hydrolysis of waste polyamide 6, using the device for gradient hydrolysis of waste polyamide 6 as described above, with the following specific steps:

[0060] (1) Preparation of raw materials;

[0061] Waste polyamide 6 melt: relative viscosity is 4.0, number average molecular weight is 40000g / mol;

[0062] (2) Superheated water vapor with a temperature of 300° C. is transported into the cylinder from the superheated water vapor through hole at the bottom of the cylinder at a transport rate of 150 kg / h, and waste polyamide 6 melt is transported into the cylinder from the melt inlet at a transport rate of 50 kg / h, and the melt in the melt storage cavity surrounded by each hydrolysis tray and the cylinder is collected to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees;

[0063] The size parameters of the device for gradient hydrolysis of waste polyamide 6 are as follows: n is 10, the distance between two adjacent hydrolysis tower plates is 10 cm, the thickness of the hydrolysis tower plate is 10 mm, the cone angle is 80°, the height of the cone is 30 cm, the aperture of the superheated water vapor through hole on the hydrolysis tower plate is 100 mesh, and the distribution density of the superheated water vapor through hole on the hydrolysis tower plate is 20 / cm 3 , m is 10, the number of melt delivery pipes b is 4, the aspect ratio of the cylinder is 10, and the distribution density of the truncated cone-shaped superheated water vapor holes on the top and bottom of the cylinder is 20 / cm 3 The upper base diameter of the truncated cone is 5 mm, and the lower base diameter of the truncated cone is 10 mm.

[0064] The relative viscosity of hydrolysate 1 is 3.6, the relative viscosity of hydrolysate 2 is 3.2, the relative viscosity of hydrolysate 3 is 2.7, the relative viscosity of hydrolysate 4 is 2.3, the relative viscosity of hydrolysate 5 is 1.9, the relative viscosity of hydrolysate 6 is 1.6, the relative viscosity of hydrolysate 7 is 1.4, the relative viscosity of hydrolysate 8 is 1.2, the relative viscosity of hydrolysate 9 is 1.1, and the relative viscosity of hydrolysate 10 is 1.

Claims

1. A device for gradient hydrolysis of waste polyamide 6, characterized in that: It comprises a cylinder and n hydrolysis tower plates arranged in a spaced manner from top to bottom in the cylinder, where n≥2; The hydrolysis tower plate is provided with a superheated water vapor through hole, and the aperture of the superheated water vapor through hole is ≥100 mesh; The hydrolysis tower plate is a conical plate, the tip of which is the highest point and the edge of which is sealed and connected to the cylinder body, and the hydrolysis tower plate and the cylinder body form a melt storage chamber; A drainage device is provided between two adjacent hydrolysis trays, and the drainage device is used to drain the melt in the melt storage cavity surrounded by the upper hydrolysis tray and the cylinder to the outside of the cylinder or the tip of the lower hydrolysis tray; Each set of drainage device includes m evenly distributed three-way valves, m≥4; the inlet of each three-way valve is connected to the melt storage cavity, one outlet is connected to the inlet of a melt outlet pipe located outside the cylinder, and the other outlet is connected to the inlet of a melt delivery pipe a located inside the cylinder; In the same set of drainage devices, the outlets of all melt conveying pipes a converge into a single outlet, and all melt conveying pipes a form a funnel-shaped structure; The melt storage cavity formed by the nth hydrolysis tray and the cylinder is connected to the inlet of at least one melt delivery pipe b located in the cylinder, and the outlet of the melt delivery pipe b is connected to the outside of the cylinder; The top of the cylinder is provided with a superheated steam through hole and a melt inlet, the melt inlet is directly opposite to the tip of the hydrolysis tower plate located at the top, and the bottom of the cylinder is provided with a superheated steam through hole.

2. The device for gradient hydrolysis of waste polyamide 6 according to claim 1, characterized in that: The distance between two adjacent hydrolysis trays is 10~15cm; 5≤n≤10; the distribution density of the superheated water vapor holes on the hydrolysis tray is ≥5 / cm 3 .

3. The device for gradient hydrolysis of waste polyamide 6 according to claim 1, characterized in that: The thickness of the hydrolysis tower plate is 10~20mm, the conical plate is conical, the cone angle is 30~80°, and the height is 30~100cm.

4. The device for gradient hydrolysis of waste polyamide 6 according to claim 3, characterized in that: All hydrolysis trays are coaxial.

5. The device for gradient hydrolysis of waste polyamide 6 according to claim 1, characterized in that: The distribution density of the superheated steam holes on the top and bottom of the cylinder is ≥5 / cm 3 The shape of the superheated steam through hole on the top and bottom of the cylinder is a truncated cone, the diameter of the upper bottom of the truncated cone is 1~5mm, the diameter of the lower bottom is 5~10mm, and the upper bottom is located above the lower bottom.

6. The device for gradient hydrolysis of waste polyamide 6 according to claim 1, characterized in that: The cylinder is cylindrical, with an operating temperature range of 25~300℃, an upper pressure limit of 10MPa, and an aspect ratio of 3~10.

7. A method for gradient hydrolysis of waste polyamide 6 using the device for gradient hydrolysis of waste polyamide 6 as described in any one of claims 1 to 6, characterized in that: Superheated water vapor is transported into the cylinder from the superheated water vapor through hole at the bottom of the cylinder, and waste polyamide 6 melt is transported into the cylinder from the melt inlet, and the melt in the melt storage cavity surrounded by each hydrolysis plate and the cylinder is collected to obtain hydrolysis products of waste polyamide 6 with different hydrolysis degrees.

8. The method for gradient hydrolysis of waste polyamide 6 according to claim 7, characterized in that: The temperature of the superheated steam is 220~300℃, the conveying speed is 20~150kg / h, and the input pressure is 0.5~3MPa; the relative viscosity of the waste polyamide 6 melt is 4.0~2.4, the number average molecular weight is 40000~12000g / mol, and the conveying speed is 20~50kg / h.

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