Method for efficiently hydrolyzing nylon 6 by acid catalysis

Abstract

The invention relates to a method for efficiently hydrolyzing nylon 6 by acid catalysis, and relates to the technical field of hydrolysis of nylon 6, the method comprises the following steps: carrying out hydrolysis reaction on nylon 6, water and an acid catalyst in a closed state to obtain a hydrolysis product; and carrying out purification post-treatment on the hydrolysis product to obtain caprolactam, the reaction pressure of the hydrolysis reaction is controlled in a self-boosting manner; the specific process of the self-boosting mode comprises the step of changing the pressure of the hydrolysis reaction system by adjusting the adding mode of the water. The nylon 6 hydrolysis process provided by the invention is simple, hydrolysis reaction pressure is controlled mainly by a self-boosting control method of a reaction system by controlling a water adding mode, other raw materials do not need to be added, efficient hydrolysis of nylon 6 is realized, and the nylon 6 hydrolysis process has the characteristics of short hydrolysis reaction time, high depolymerization rate and the like, and is suitable for industrial production. The method effectively solves the technical problems of long hydrolysis reaction time and low depolymerization rate in the existing process for catalyzing and hydrolyzing nylon 6 by using an acid method.

Description

Technical Field

[0001] The present application relates to the technical field of nylon 6 hydrolysis, and in particular to a method for efficient hydrolysis of nylon 6 catalyzed by acid. Background Art

[0002] Polyamide 6, commonly known as nylon 6 (PA6), is a crystalline polymer with good comprehensive properties and is one of the most widely used varieties of engineering plastics. Nylon 6 chips, also known as nylon 6 chips, are the second largest chemical fiber in synthetic fibers and play an important role in industrial use. With its continuous application in many fields, its products are difficult to handle after use, which not only causes waste but also pollutes the environment. Therefore, recycling high temperature resistant nylon 6 has significant economic and social benefits.

[0003] At present, the recycling of nylon 6 mainly adopts the method of chemical recycling, mainly including hydrolysis and alcoholysis. The hydrolysis method is a method of catalytic cracking by adding a catalyst, and then the hydrolyzate after cracking the nylon 6 slice is subjected to extraction and vacuum distillation and other purification post-processing steps to obtain caprolactam monomer and recover the organic solvent. Among them, the hydrolysis method mainly includes alkaline catalytic hydrolysis and acid catalytic hydrolysis, but in the prior art, whether it is acid catalytic hydrolysis or other catalytic depolymerization methods, there are certain defects, or the hydrolysis time is long, or the hydrolysis temperature is high, or the yield is low, or the process conditions are complicated, or the process conditions are difficult to control, etc. The above defects lead to high recovery costs of nylon 6, which is not conducive to the forward treatment of nylon 6 recovery. Summary of the invention

[0004] The present application provides a method for efficient hydrolysis of nylon 6 by acid catalysis, so as to solve the technical problems of long hydrolysis reaction time and low depolymerization rate in the existing acid catalytic hydrolysis process of nylon 6.

[0005] The present application provides a method for efficient hydrolysis of nylon 6 catalyzed by acid, the method comprising the following steps:

[0006] The nylon 6, water and acid catalyst are subjected to a hydrolysis reaction in a closed state to obtain a hydrolysis product;

[0007] Purifying the hydrolyzate to obtain caprolactam;

[0008] The reaction pressure of the hydrolysis reaction is controlled by a self-pressurization method;

[0009] The specific process of the self-pressurization method includes: changing the pressure of the hydrolysis reaction system by adjusting the water addition method.

[0010] Furthermore, the water is added in batches in stages to achieve gradient regulation of the pressure of the hydrolysis reaction system.

[0011] Furthermore, based on the weight of the nylon 6, the specific process of adding in stages in batches includes:

[0012] At the beginning of the hydrolysis reaction, the weight of the water added to the reaction system for the first time is 25%-500% of the weight of the nylon 6;

[0013] 0.3h-1.0h after the hydrolysis reaction begins, the weight of the water added to the reaction system for the second time is 25%-500% of the weight of the nylon 6.

[0014] Furthermore, the weight of the water added for the first time is 150%-200% of the weight of the nylon 6; the weight of the water added for the second time is 150%-200% of the weight of the nylon 6; the temperature of the water added for the second time is 60°C-80°C.

[0015] Furthermore, the specific process of the self-pressurization method also includes: adjusting the temperature of the hydrolysis reaction to coordinate the water addition method, so as to achieve the control of the reaction pressure of the hydrolysis reaction by the self-pressurization method.

[0016] Furthermore, the weight ratio of the nylon 6, the water and the acid catalyst is 1:(0.5-10):(0.02-0.4).

[0017] Furthermore, the working parameters of the hydrolysis reaction include: reaction temperature of 150°C to 400°C, reaction time of 0.5h to 4h, and reaction pressure of 0.5Mpa to 3.0Mpa.

[0018] Further, the acid catalyst includes at least one of benzenesulfonic acid, p-toluenesulfonic acid, hypophosphorous acid, phosphoric acid, superphosphoric acid, sulfuric acid and persulfuric acid.

[0019] Furthermore, the step of purifying the hydrolyzate to obtain caprolactam comprises:

[0020] The hydrolyzate is dried and then crushed to obtain a powdered hydrolyzate;

[0021] extracting the powdered hydrolyzate with an organic solvent to obtain an organic extraction phase;

[0022] The organic extract phase is distilled under reduced pressure to obtain caprolactam.

[0023] Furthermore, the depolymerization rate of nylon 6 is greater than 90%, and the yield of caprolactam is greater than 75%.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The embodiment of the present application provides a method for efficient hydrolysis of nylon 6 catalyzed by acid. The method adopts an acid-catalyzed hydrolysis method, and the hydrolysis process is simple. In a closed environment, the water-saturated steam in the reaction system can increase the reaction pressure in the kettle. The hydrolysis reaction pressure is controlled mainly by controlling the amount of water added to the reaction system through a self-pressurization control method. No other raw materials need to be added, and efficient hydrolysis of nylon 6 is achieved. The method is simple to operate and has the characteristics of short hydrolysis reaction time and high depolymerization rate. The technical problems of long hydrolysis reaction time and low depolymerization rate in the existing acid-catalyzed hydrolysis process of nylon 6 are effectively solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 A schematic flow chart of a method for efficient hydrolysis of nylon 6 by acid catalysis provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0031] The present application provides a method for the efficient hydrolysis of nylon 6 catalyzed by acid, such as Figure 1 As shown, the method comprises the following steps:

[0032] The nylon 6, water and acid catalyst are subjected to a hydrolysis reaction in a closed state to obtain a hydrolysis product;

[0033] Purifying the hydrolyzate to obtain caprolactam;

[0034] The reaction pressure of the hydrolysis reaction is controlled by a self-pressurization method;

[0035] The specific process of the self-pressurization method includes: changing the pressure of the hydrolysis reaction system by adjusting the water addition method.

[0036] The embodiment of the present application provides a method for efficient hydrolysis of nylon 6 catalyzed by acid. The method adopts an acid-catalyzed hydrolysis method, and the hydrolysis process is simple. In a closed environment, the water-saturated steam in the reaction system can increase the reaction pressure in the kettle. The hydrolysis reaction pressure is controlled mainly by controlling the amount of water added to the reaction system through a self-pressurization control method. No other raw materials need to be added, and efficient hydrolysis of nylon 6 is achieved. The method is simple to operate and has the characteristics of short hydrolysis reaction time and high depolymerization rate. The technical problems of long hydrolysis reaction time and low depolymerization rate in the existing acid-catalyzed hydrolysis process of nylon 6 are effectively solved.

[0037] In addition, the reaction process of the present invention is in a closed state, and the pressure in the reaction system is almost close to the saturated vapor pressure of water in a subcritical state. Subcritical water is rich in hydrogen ions and hydroxide ions, which can play a certain role as an acidic catalyst or a basic catalyst. At the same time, under the dual conditions of acidity and subcriticality, the catalytic performance of the catalyst can be promoted, thereby further improving the hydrolysis rate of nylon 6, and further improving the depolymerization rate and shortening the depolymerization time.

[0038] In some specific embodiments, the nylon 6 described in the present application mainly includes waste nylon 6, such as recycled nylon 6 powder, pellets, foam materials, fiber materials or any mixture of the above from different sources.

[0039] In some specific embodiments, the process of obtaining the hydrolysis product further includes: cooling the hydrolysis reaction system to room temperature after the hydrolysis reaction is completed, and rapidly reducing the pressure to normal pressure, so as to facilitate subsequent purification of the hydrolysis product.

[0040] In some specific embodiments, the specific implementation process of obtaining the hydrolyzate of the present application may include: placing nylon 6, water and an acid catalyst in a closed autoclave, and carrying out a depolymerization reaction under continuous stirring conditions; after the hydrolysis reaction is completed, taking out the hydrolyzate of the autoclave, and cooling it in cold water, the pressure is rapidly reduced to normal pressure, and after cooling to room temperature, subsequent hydrolyzate purification and post-treatment steps are carried out. The above-mentioned autoclave can use existing equipment; preferably, an existing autoclave equipment with a motor, a stirring shaft and multi-layer blades can be used, and the stirring shaft and the multi-layer blades are driven by the motor to rotate to achieve stirring, mixing and flow of the liquid phase in the reactor; the multi-layer blades can be a combination of 2 or more layers of blades to achieve sufficient stirring of the entire reaction system.

[0041] In some specific embodiments, the post-purification treatment method for the hydrolyzate of the present application can be carried out according to the contents disclosed in the prior art, such as performing post-purification treatment steps such as extraction and reduced pressure distillation on the hydrolyzate to achieve the purpose of obtaining caprolactam monomer and recovering organic solvent.

[0042] In some specific embodiments, the purity of caprolactam obtained by the method provided in the present application can be above 99.5% by mass, and the contents of cyclic dimer and trimer thereof are respectively less than 0.3% and 0.2%.

[0043] As an implementation method of an embodiment of the present application, the water is added in stages and batches to achieve gradient regulation of the pressure of the hydrolysis reaction system.

[0044] The present application adopts phased batch addition, and in a closed environment, utilizes the water-saturated steam in the reaction system to achieve gradient increase and maintain the reaction pressure of the reaction system, without adding other raw materials, to achieve efficient hydrolysis of nylon 6, and the operation is simple.

[0045] In some specific embodiments, the phased batch addition described in the present application can be carried out in two-stage batch addition or three-stage batch addition. For example, a certain amount of water is added before the hydrolysis reaction begins, and then an appropriate amount of water is added after a period of reaction to increase the pressure of the reaction system in a gradient manner, thereby further maintaining and improving the depolymerization rate until the hydrolysis reaction is completed.

[0046] As an implementation method of the present application, based on the weight of the nylon 6, the specific process of adding in batches in stages includes:

[0047] At the beginning of the hydrolysis reaction, the weight of the water added to the reaction system for the first time is 25%-500% of the weight of the nylon 6;

[0048] 0.3h-1.0h after the hydrolysis reaction begins, the weight of the water added to the reaction system for the second time is 25%-500% of the weight of the nylon 6.

[0049] The applicant has found through extensive practice that the above-mentioned specific method (including the amount of water added for the first time in the initial reaction system, the time point for the second addition of water, and the amount of water added for the second time) is used to add water to the reaction system in batches, which is more effective and conducive to the hydrolysis reaction, and the hydrolysis reaction is more efficient.

[0050] In some specific embodiments, at the beginning of the hydrolysis reaction, the weight of the water added for the first time may be 25%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, 400%, 410%, 420%, 430%, 440%, 450%, 460%, 470%, 480%, 490%, 500%, 510%, 520%, 530%, 540%, 550%, 560%, 570%, 580%, 590%, 600%, 610%, 620%, 630%, 640%, 650%, 660%, 670%, 680%, 690%, 700%, 710%, 720%, 730%, 740%, 750%, 760%, 770%, 780%, 790%, 800%, 810%, 820%, 830%, 840%, 850%, 860%, 870%, 880%, 890%, 900%, 910%, 920%, 930%, 940%, 950%, 960%, 970%, 980%, 990 %, 90%, 300%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, 400%, 410%, 420%, 430%, 440%, 450%, 460%, 470%, 480%, 490%, 500% and the like; preferably, the weight of the water added for the first time is 150%-250% of the weight of the nylon 6, more preferably, the weight of the water added for the first time is 200% of the weight of the nylon 6.

[0051] In some specific embodiments, the time point for adding the water for the second time may be 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, etc. from the start of the hydrolysis reaction; preferably, the time point for adding the water for the second time is 0.5h-1.0h, more preferably 0.7h from the start of the hydrolysis reaction.

[0052] In some specific embodiments, the weight of the water added for the second time can be 25%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, 400%, 410%, 420%, 430%, 440%, 450%, 460%, 470%, 480%, 490%, 500%, 510%, 520%, 530%, 540%, 550%, 560%, 570%, 580%, 590%, 600%, 610%, 620%, 630%, 640%, 650%, 660%, 670%, 680%, 690%, 700%, 710%, 720%, 730%, 740%, 750%, 760%, 770%, 780%, 790%, 800%, 810%, 820%, 830%, 840%, 850%, 860%, 870%, 880%, 890%, 900%, 910%, 920%, 930%, 940%, 950%, 960%, 970%, 980%, 990%, 1000%, 1 0%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, 400%, 410%, 420%, 430%, 440%, 450%, 460%, 470%, 480%, 490%, 500% and the like; preferably, the weight of the water added for the second time is 150%-250% of the weight of the nylon 6, more preferably, the weight of the water added for the second time is 200% of the weight of the nylon 6.

[0053] As an implementation method of the present application, the temperature of the water added for the second time is 60°C to 80°C.

[0054] The purpose of controlling the temperature of the second water added to be 60°C to 80°C in the present application is to supplement the medium and raw materials required for the reaction, improve the heat and mass transfer capacity of the system, and regulate the reaction temperature and pressure; if the temperature of the second water added is too high or too low, the adverse effect is that it causes large fluctuations in the temperature and pressure of the reaction system, affecting the chain breaking behavior of nylon 6 and the process of dehydration cyclization of oligomers into the target product caprolactam.

[0055] As an implementation method of an embodiment of the present application, the specific process of the self-pressurization method also includes: adjusting the temperature of the hydrolysis reaction to coordinate the water addition method to achieve the control of the reaction pressure of the hydrolysis reaction by the self-pressurization method.

[0056] The reaction pressure of the hydrolysis reaction system of the present application is established by the method of self-pressurization of the system. On the basis of the above-mentioned method of mainly controlling the amount of water added, the temperature of the hydrolysis reaction can also be adjusted to further control the reaction pressure by adjusting the reaction temperature. In addition, in some specific embodiments, in addition to regulating the pressure of the reaction system by self-pressurization, the present application can also control the pressure of the reaction system in combination with an external pressure control method, such as cooperating with a gas phase pressure regulating valve at the top of the reactor to change the pressure of the reaction system.

[0057] As an implementation method of the example of the present application, the weight ratio of the nylon 6, the water and the acid catalyst is 1:(0.5-10):(0.02-0.4).

[0058] The above-mentioned “the weight ratio of the nylon 6, the water and the acid catalyst is 1:(0.5-10):(0.02-0.4)” in the present application can also be expressed as “based on the weight of the nylon 6, the added weight of the water is 50%-1000% of the weight of the nylon 6, and the added weight of the acid catalyst is 2%-40% of the weight of the nylon 6”.

[0059] Based on the weight of the nylon 6, the purpose of controlling the weight of the added water to be 50% to 1000% of the weight of the nylon 6 in the present application is to ensure sufficient contact between nylon 6 and water and to ensure sufficient reaction; if the weight of the added water is too much or too little, the adverse effect is that too little water can easily lead to carbonization or side reactions, and too much water has little effect on the hydrolysis reaction and can easily cause waste of resources.

[0060] In some specific embodiments, based on the weight of the nylon 6, the added weight of the water is preferably 150% to 500% of the weight of the nylon 6, specifically 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, 400%, 410%, 420%, 430%, 440%, 450%, 460%, 470%, 480%, 490%, 500% and the like.

[0061] Based on the weight of the nylon 6, the purpose of controlling the added weight of the acid catalyst to be 2% to 40% of the weight of the nylon 6 in the present application is to provide good acidic conditions for the reaction, effectively catalyze the occurrence of the forward depolymerization reaction of nylon 6, and accelerate the reaction process; if the added weight of the acid catalyst is too much or too little, the adverse effect is that too little catalyst cannot effectively catalyze the chain breaking of nylon 6 and the generation of the target monomer; the addition of excessive catalyst strengthens the corrosion effect on the equipment, which is not conducive to subsequent production.

[0062] In some specific embodiments, based on the weight of the nylon 6, the added weight of the acid catalyst is preferably 10%-25% of the weight of the nylon 6, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% and the like.

[0063] In some specific embodiments, the present application selects the acid catalyst itself to have a mass percentage concentration of 60% to 99%, and its function is to ionize H in water. + , providing good acidic conditions to accelerate the chain scission of nylon 6 segments and the dehydration cyclization of oligomers to generate the target monomer caprolactam; preferably 80% to 95%, specifically 80%, 81%, 82%, 83%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0064] As an implementation method of an embodiment of the present application, the working parameters of the hydrolysis reaction include: a reaction temperature of 150°C to 400°C, a reaction time of 0.5h to 4h, and a reaction pressure of 0.5Mpa to 3.0Mpa.

[0065] The purpose of controlling the reaction temperature to 150°C to 400°C in this application is to increase the activity of the polyamide molecular chain and promote the ionization of water molecules and acidic catalysts to generate H +, so that the amide bond breaks; preferably 200℃~300℃, specifically 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.

[0066] The purpose of controlling the reaction time to 0.5h to 4h in the present application is to ensure that nylon 6 has sufficient reaction time with water and that the oligomer has sufficient time for dehydration and cyclization to form the target product caprolactam; preferably, the reaction time is 1.5h to 3.0h, and specifically can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h, 4.0h, etc.

[0067] The purpose of controlling the reaction pressure to 0.5Mpa to 3.0Mpa in the present application is to maintain the reaction rate and equilibrium state and ensure the progress of the reaction process; preferably, it is 1.0Mpa to 1.8Mpa.

[0068] As an implementation of an example of the present application, the acid catalyst includes at least one of benzenesulfonic acid, p-toluenesulfonic acid, hypophosphorous acid, phosphoric acid, superphosphoric acid, sulfuric acid and persulfuric acid.

[0069] The present invention uses at least one of benzenesulfonic acid, p-toluenesulfonic acid, hypophosphorous acid, phosphoric acid, superphosphoric acid, sulfuric acid and persulfuric acid as a catalyst to ionize H in water. + , which is beneficial to the breaking of the CN bond of the amide group, accelerates the chain breaking of the nylon 6 segment and the dehydration cyclization of the oligomer to generate the target monomer caprolactam, speeds up the reaction and improves the depolymerization efficiency.

[0070] As an implementation method of the present application, the step of purifying the hydrolyzate to obtain caprolactam comprises:

[0071] The hydrolyzate is dried and then crushed to obtain a powdered hydrolyzate;

[0072] extracting the powdered hydrolyzate with an organic solvent to obtain an organic extraction phase;

[0073] The organic extract phase is distilled under reduced pressure to obtain caprolactam.

[0074] In some specific embodiments, the above steps may specifically include:

[0075] The hydrolyzate is dried and crushed into powder under vacuum conditions, and then subjected to Soxhlet extraction with an organic solvent. After continuous heating and extraction for 12 hours, the liquid phase is recovered; the organic solvent is a lower alcohol with a mass percentage concentration of 85% to 99%. The lower alcohol includes methanol, ethanol, propanol, etc.

[0076] The extracted phase is subjected to reduced pressure distillation to recover the extractant, thereby obtaining high-purity caprolactam (purity above 99.5%) and a small amount of cyclic dimer (less than 0.3%) and trimer (less than 0.2%).

[0077] It should be noted that the above-mentioned Soxhlet extraction and vacuum distillation operations in this application, unless otherwise specified or limited, can be performed using conventional existing technologies in the art, and this application document will not describe them one by one.

[0078] As an implementation of an example of the present application, the depolymerization rate of nylon 6 is greater than 90%, and the yield of caprolactam is greater than 75%.

[0079] The depolymerization rate of nylon 6 described in the present application is greater than 90%, and the yield of caprolactam is greater than 75%, and the present application has the characteristics of high depolymerization rate of nylon 6 and high yield of caprolactam.

[0080] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0081] Example 1

[0082] This embodiment provides a method for efficient hydrolysis of nylon 6 catalyzed by acid, the method comprising:

[0083] Nylon 6 chips, water and phosphoric acid solution are placed in a closed autoclave, and the temperature in the autoclave is set to 180° C. and the reaction pressure is set to 1.0 MPa. The amount of water added for the first time at the beginning of the reaction is 50% by weight of the nylon 6 chips, the concentration of the phosphoric acid solution is 85%, and the amount added is 30% by weight of the weight of the nylon 6 chips. The magnetic stirring is turned on, and the speed is 400 r / min. After reacting for 30 minutes, pure water at a temperature of 80° C. is added for the second time, and is slowly added through the feeding port on the top of the autoclave. The amount of water added for the second time is 50% by weight of the weight of the nylon 6 chips. The reaction is continued for 1 hour, and the hydrolysis reaction is completed;

[0084] Place the autoclave in cold water, and quickly reduce the pressure inside the autoclave to normal pressure. After reaching room temperature, take out the hydrolysis product in the autoclave;

[0085] The hydrolyzate was dried and crushed into powder under vacuum conditions, and Soxhlet extraction was performed using methanol. The liquid phase was recovered after continuous heating and extraction for 12 hours; the mass percentage concentration of methanol was 85%;

[0086] The extracted phase is subjected to reduced pressure distillation to recover the extractant, thereby obtaining high-purity caprolactam (purity>99.5) and a small amount of cyclic dimer (<0.3%) and trimer (<0.2%).

[0087] In the present embodiment, vacuum distillation can be realized by using prior art. The specific processing method of the Soxhlet extraction technology used in the extraction includes: weighing about 3g of cracking product powder, placing it in the middle section of the Soxhlet extractor after wrapping with quantitative filter paper, adding about 150mL of methanol to a round-bottomed flask, and continuously heating and extracting for 12 hours. After the extraction is completed, all liquid phases in the Soxhlet extractor are recovered and settled to a 250mL volumetric flask. Since the solution concentration is still higher than the liquid chromatography analysis range at this time, errors may be caused, therefore, it is still necessary to accurately transfer 2mL to a 25mL volumetric flask with a pipette, and finally inject it into a 2mL liquid chromatography analysis sample bottle after filtration, and analyze the depolymerization rate with high performance liquid chromatography.

[0088] High performance liquid chromatography: Waters high performance liquid chromatography (HPLC) analysis system, Breeze data processing system. Chromatographic column: Waters C18 liquid chromatography column. Analysis wavelength: 210 nm. Mobile phase: methanol (chromatographic grade), water (ultrapure water) in a gradient ratio.

[0089] In this Example 1, the caprolactam yield was 78.7% and the depolymerization rate of nylon 6 was 91.8%.

[0090] Example 2-8 investigates the effect of the temperature in the autoclave on the hydrolysis of nylon 6.

[0091] On the basis of Example 1, Examples 2-8 only adjusted the temperature in the autoclave (the remaining steps and parameters were the same as those in Example 1). The specific temperatures in the autoclave in Examples 2-8 are shown in Table 1.

[0092] Table 1 Example 2-7 Investigating the effect of temperature in the autoclave on the hydrolysis of nylon 6

[0093]

[0094] Examples 9-19 investigate the effect of phased batch addition of water on the hydrolysis of nylon 6.

[0095] On the basis of Example 1, Examples 9-18 only adjusted the phased batch addition method of water (the remaining steps and parameters were the same as those of Example 1). The phased batch addition method of water in Examples 9-18 is shown in Table 2, and the test results are shown in Table 3; wherein, the initial first water addition amount and the second water addition amount in each example are both calculated as "percentage of the weight of nylon 6 chips"; the total reaction time in each example is 1.5h (90min), that is, if the time node of the second water addition is adjusted, the subsequent reaction time of the second water addition is adjusted accordingly based on the total reaction time of 1.5h; for example, if the second water addition time is after 40min of reaction, the subsequent reaction is continued for 50min, and the hydrolysis reaction is terminated.

[0096] Table 2 Phased batch addition of water in Examples 9-18

[0097]

[0098]

[0099] Table 3 Caprolactam yield and nylon 6 depolymerization rate results in Examples 9-18

[0100]

[0101] Embodiment 19

[0102] In this embodiment, water is added in batches in three stages. The difference from Example 1 is that nylon 6 chips, water and phosphoric acid solution are placed in a closed autoclave, the temperature in the autoclave is set to 180° C., the amount of water is 50% of the nylon 6 chips, the concentration of the phosphoric acid solution is 85%, and the amount added is 30% of the mass of the nylon 6 chips. The magnetic stirring is turned on, the speed is 300-500 r / min, and after reacting for 60 minutes, pure water with a temperature of 60-80° C. is added slowly through the feeding port on the top of the autoclave, the amount of water added twice is 50% of the mass of the nylon 6 chips, and the reaction is continued for 1 hour. Pure water with a temperature of 60-80° C. is added three times, and the amount of water added is 100% of the mass of the nylon 6 chips. The reaction is continued for 2 hours, and the hydrolysis reaction is terminated; the autoclave is placed in cold water, the pressure in the autoclave is quickly reduced to normal pressure, and the hydrolysis product in the autoclave is taken out after reaching room temperature; the remaining steps and parameters are the same.

[0103] In this example, the caprolactam yield was 84.5%, and the depolymerization rate of nylon 6 was 94.4%.

[0104] Examples 20-24 investigate the effect of reaction time on the hydrolysis of nylon 6.

[0105] Based on Example 1, Examples 20-24 only adjust the continued reaction time after the second addition of water (the remaining steps and parameters are the same as Example 1). The continued reaction time after the second addition of water in Examples 20-24 is shown in Table 4.

[0106] Table 4: Effect of reaction time on nylon 6 hydrolysis in Examples 20-24

[0107]

[0108] Examples 25-28 investigate the effect of acid catalysts on the hydrolysis of nylon 6.

[0109] On the basis of Example 1, Examples 25-28 only adjusted the acid catalyst (the remaining steps and parameters were the same as in Example 1). The specific types and amounts of the acid catalysts in Examples 25-28 are shown in Table 5; wherein the amount of the acid catalyst in each example is measured as "percentage of the weight of nylon 6 chips".

[0110] Table 5 Examples 25-28 Investigating the effect of acid catalyst on nylon 6 hydrolysis

[0111]

[0112] Comparative Example 1

[0113] The difference between this example and Example 1 is that nylon 6 chips, water and phosphoric acid solution are placed in a high-pressure reactor, the temperature in the high-pressure reactor is set to 180° C., the reaction pressure is 1.0 MPa, the amount of water added to the reaction is 100% by weight of the nylon 6 chips, the concentration of the phosphoric acid solution is 85%, the amount added is 30% by weight of the weight of the nylon 6 chips, the magnetic stirring is turned on, the speed is 400 r / min, and the hydrolysis reaction ends after the reaction for 90 minutes; the remaining steps and parameters are the same.

[0114] Compared with Example 1, after the reaction of Comparative Example 1 was completed, the caprolactam yield was 72.4%, and the nylon 6 depolymerization rate was 87.3%.

[0115] In summary, the embodiment of the present application provides a method for efficient hydrolysis of nylon 6 catalyzed by acid, which adopts an acid-catalyzed hydrolysis method, has a simple hydrolysis process, and in a closed environment, the water-saturated steam in the reaction system can increase the reaction pressure in the kettle, and the hydrolysis reaction pressure is controlled mainly by controlling the amount of water added to the reaction system by a self-pressurization control method, without adding other raw materials, to achieve efficient hydrolysis of nylon 6, simple operation, short hydrolysis reaction time and high depolymerization rate, etc., and effectively solves the technical problems of long hydrolysis reaction time and low depolymerization rate in the existing acid-catalyzed hydrolysis process of nylon 6.

[0116] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0117] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0118] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for efficient hydrolysis of nylon 6 catalyzed by acid, characterized in that: The method comprises the following steps: The nylon 6, water and acid catalyst are subjected to a hydrolysis reaction in a closed state to obtain a hydrolysis product; Purifying the hydrolyzate to obtain caprolactam; The reaction pressure of the hydrolysis reaction is controlled by a self-pressurization method; The specific process of the self-pressurization method includes: changing the pressure of the hydrolysis reaction system by adjusting the water addition method.

2. The method according to claim 1, characterized in that The water is added in batches in stages to achieve gradient regulation of the pressure of the hydrolysis reaction system.

3. The method according to claim 2, characterized in that The specific process of adding in batches in stages includes: At the beginning of the hydrolysis reaction, the weight of the water added to the reaction system for the first time is 25%-500% of the weight of the nylon 6; 0.3h-1.0h after the hydrolysis reaction starts, the weight of the water added to the reaction system for the second time is 25%-500% of the weight of the nylon 6.

4. The method according to claim 3, characterized in that: The weight of the water added for the first time is 150%-200% of the weight of the nylon 6; the weight of the water added for the second time is 150%-200% of the weight of the nylon 6; the temperature of the water added for the second time is 60°C-80°C.

5. The method according to any one of claims 1 to 4, characterized in that: The specific process of the self-pressurization method also includes: adjusting the temperature of the hydrolysis reaction to match the water addition method to achieve the control of the reaction pressure of the hydrolysis reaction by the self-pressurization method.

6. The method according to any one of claims 1 to 4, characterized in that: The weight ratio of the nylon 6, the water and the acid catalyst is 1:(0.5-10):(0.02-0.4).

7. The method according to any one of claims 1 to 4, characterized in that: The working parameters of the hydrolysis reaction include: reaction temperature of 150° C. to 400° C., reaction time of 0.5 h to 4 h, and reaction pressure of 0.5 Mpa to 3.0 Mpa.

8. The method according to any one of claims 1 to 4, characterized in that: The acid catalyst includes at least one of benzenesulfonic acid, p-toluenesulfonic acid, hypophosphorous acid, phosphoric acid, superphosphoric acid, sulfuric acid and persulfuric acid.

9. The method according to any one of claims 1 to 4, characterized in that: The step of purifying the hydrolyzate to obtain caprolactam comprises: The hydrolyzate is dried and then crushed to obtain a powdered hydrolyzate; extracting the powdered hydrolyzate with an organic solvent to obtain an organic extraction phase; The organic extract phase is distilled under reduced pressure to obtain caprolactam.

10. The method according to any one of claims 1 to 4, characterized in that: The depolymerization rate of the nylon 6 is greater than 90%, and the yield of the caprolactam is greater than 75%.

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