Recovery method of nylon

Abstract

The invention belongs to the field of plastic chemical recovery, and particularly relates to a nylon recovery method. The recycling method of the nylon comprises microwave depolymerization, wherein the microwave depolymerization comprises the step of adding the nylon, a catalyst and an optionally added microwave absorption accelerant into a microwave reactor for depolymerization reaction. The method has the advantages of mild recovery condition, short reaction time, simple product, suitability for continuous production in depolymerization and separation processes, and the like.

Description

Technical Field

[0001] The invention belongs to the field of plastic chemical recycling, and in particular relates to a nylon recycling method. Background Art

[0002] Nylon, also known as polyamide, is a commonly used plastic. The global market currently produces more than 8 million tons per year, and this figure is expected to grow at a rate of 2.2%, reaching 10.4 million tons by 2027, with an output value of approximately US$47 billion. However, the growth in nylon consumption and its non-biodegradable properties have led to land and ocean pollution, posing a serious threat to the ecosystem. Therefore, the recycling and reuse technology of waste nylon has attracted widespread attention.

[0003] The main ways to recycle waste nylon include energy recovery, physical recovery and chemical recovery. Energy recovery mainly adopts the method of incineration. Although this method is easy to operate, it has low added value and increases carbon emissions, which will pollute the air and cause environmental pollution. Physical recovery includes primary mechanical recovery and secondary physical recovery. The quality of recycled products cannot be guaranteed and the number of recovery times is limited. Chemical recovery involves the depolymerization of waste nylon. The main purpose is to degrade waste nylon into monomers with higher value and use them again in nylon production. It is a sustainable recovery model.

[0004] Common chemical recovery technologies include hydrolysis, alcoholysis, ammonialysis, etc.

[0005] Patent document CN1257880C reports a method for producing adipic acid and hexamethylenediamine by depolymerization of nylon 66, which consists of an acidolysis stage, a cooling crystallization stage, an acid separation stage, a recrystallization stage, a neutralization stage, and a refining stage. Nylon 66 is acidolyzed for 6-16 hours under a pressure of 0.1-0.6 MPa to obtain adipic acid, which is then neutralized by adding alkali to obtain hexamethylenediamine. The acid used in the acidolysis stage is sulfuric acid, and the alkali used for neutralization is lime milk. This method has problems such as long reaction time and harsh reaction conditions.

[0006] Patent document US5266694A reports that in the presence of alkali, nylon 66 can be hydrolyzed at 250-400°C for at least 4 hours to obtain monomers such as hexamethylenediamine, but the reaction temperature is relatively high and the reaction time is also relatively long.

[0007] Patent document CN107056624B provides a method for recovering components such as dialkyl adipate and hexamethylenediamine monomer by alcoholysis of nylon 66, alcohol and catalyst in a high-pressure reactor using an acid as a catalyst, followed by a series of extractions, vacuum distillation and other operations. This method has the problems of complex products requiring subsequent treatment, excessive alcohol usage and long reaction time.

[0008] Patent document EP675871B1 discloses the use of ammonolysis technology to recycle waste nylon mixtures, mainly by injecting ammonia into melted waste plastics and depolymerizing them at 250-400°C and 100psi. The products mainly include hexamethylenediamine, adiponitrile, 6-aminocapronitrile, etc. The obtained products still need to be further hydrogenated and reduced to be converted into hexamethylenediamine.

[0009] In summary, these chemical recovery methods have disadvantages such as long reaction time, harsh reaction conditions, high recovery cost or complex reaction products.

[0010] Therefore, there is an urgent need to develop a nylon recycling method with mild conditions, efficient recycling, simple products, and easy continuous production. Summary of the invention

[0011] In order to solve the problems existing in the prior art, the present invention provides a nylon recovery method. The present invention obtains a diacid monomer by microwave depolymerization. The recovery method of the present invention has mild conditions, high recovery efficiency, simple products, and is easy for continuous production.

[0012] Specifically, the present invention provides a nylon recovery method, which includes microwave depolymerization, wherein the microwave depolymerization includes adding nylon, a catalyst and an optionally added microwave absorption promoter into a microwave reactor for depolymerization reaction.

[0013] In one or more embodiments, the catalyst is an acid, preferably one or more selected from hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

[0014] In one or more embodiments, the mass of the catalyst is 40% to 300%, preferably 50% to 100%, of the mass of the nylon.

[0015] In one or more embodiments, the microwave absorption enhancer is selected from one or more of Na3PO4, NH4H2PO4, ZnCl2 and CuSO4.

[0016] In one or more embodiments, the mass of the microwave absorption enhancer is 0-10% of the mass of nylon.

[0017] In one or more embodiments, the microwave reactor is made of polytetrafluoroethylene and / or Si3N4.

[0018] In one or more embodiments, the microwave frequency is 915±25 MHz or 2450±25 MHz.

[0019] In one or more embodiments, the temperature of the depolymerization reaction is 150-300°C, preferably 180-250°C, and more preferably 200-230°C.

[0020] In one or more embodiments, the depolymerization reaction time is ≥5 min, preferably 5-240 min, and more preferably 10-60 min.

[0021] In one or more embodiments, the nylon is selected from one or more of nylon 66, nylon 610, nylon 612, and nylon 6T.

[0022] In one or more embodiments, the microwave reactor is made of polytetrafluoroethylene, and the temperature of the depolymerization reaction is 150-230°C.

[0023] In one or more embodiments, the microwave reactor is made of Si3N4, and the temperature of the depolymerization reaction is 150-300°C.

[0024] In one or more embodiments, the nylon is molten nylon.

[0025] In one or more embodiments, the recovery method further comprises sequentially cooling, crystallizing and filtering the product of the depolymerization reaction, refining the solid product obtained by filtration by recrystallization to obtain a diacid monomer and a diacid monomer mother liquor; and sequentially neutralizing the liquid product obtained by filtration by adding a base, extracting and separating by adding an extractant, and distilling to obtain hexamethylenediamine and a mixed solution.

[0026] In one or more embodiments, the diacid monomer is preferably selected from one or more of adipic acid, sebacic acid, dodecanedioic acid, and terephthalic acid.

[0027] In one or more embodiments, the recrystallization purification sequentially includes water washing before recrystallization, recrystallization, and separation and drying after recrystallization.

[0028] In one or more embodiments, during the process of adding alkali for neutralization, the pH end point is 10-14, preferably 11-13.

[0029] In one or more embodiments, the extractant is a mixture of an aromatic hydrocarbon and an alcohol.

[0030] In one or more embodiments, the mass ratio of the hydrolyzate obtained by neutralization with alkali to the extractant is 1:(1-5).

[0031] In one or more embodiments, the temperature of the extractive separation is 40-100°C.

[0032] In one or more embodiments, the recovery method further comprises using the diacid monomer mother liquor as a feedstock for the microwave depolymerization.

[0033] In one or more embodiments, the recovery method further comprises using the mixed solution as an extractant. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a process flow chart for recovering nylon in some embodiments of the present invention.

[0035] Figure 2 The present invention is a process flow chart for recovering nylon 66 in some embodiments of the present invention. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0037] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0038] Herein, “comprising”, “including”, “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of”. For example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to be disclosed herein.

[0039] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0040] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0041] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0042] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0043] The present invention provides a nylon recovery method, the method comprising microwave depolymerization, wherein the microwave depolymerization comprises adding nylon, a catalyst and an optionally added microwave absorption promoter into a microwave reactor for depolymerization reaction. The depolymerization reaction of the present invention is carried out in a microwave reactor, can be continuously produced, uses microwave heating as a heat source, has milder reaction conditions, higher reaction efficiency, and the depolymerization product can be directly used for polymerization reaction, thus avoiding the problem that the product of other methods is complicated and needs post-processing.

[0044] The method of the present invention is applicable to the recovery of various types of nylon (PA), especially nylon 66, nylon 610, nylon 612, and nylon 6T. The diacid monomers corresponding to nylon 66, nylon 610, nylon 612, and nylon 6T are adipic acid, sebacic acid, dodecanedioic acid, and terephthalic acid, respectively. The common point is that the solubility in water, especially in acidic aqueous solution, is very low, and can be directly separated by filtering. Therefore, all nylons with this feature are applicable to the present invention.

[0045] In the present invention, the catalyst is preferably an acid. In the present invention, the acid used as the catalyst can be one or more selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. In the present invention, the mass of the catalyst can be 40%-300% of the mass of nylon, preferably 50%-100%, such as 50%, 60%, 70%, 80%, 90%, 100%. In the present invention, controlling the ratio of the mass of the catalyst to the mass of nylon within the above range is conducive to obtaining a better depolymerization effect and improving the yield of the diacid monomer and hexamethylenediamine.

[0046] In the present invention, a microwave absorption promoter may or may not be added to the reaction system. Preferably, a microwave absorption promoter is added to the reaction system. The microwave absorption promoter may be a salt with a high absorption rate for microwaves, preferably selected from one or more of Na3PO4, NH4H2PO4, ZnCl2 and CuSO4. In the present invention, when a microwave absorption promoter is added, the mass of the microwave absorption promoter may be 0.1-10% of the mass of nylon, such as 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%. The present invention finds that adding a microwave absorption promoter to the reaction system can make the depolymerization reaction conditions relatively mild and the reaction time shorter. Controlling the amount of the microwave absorption promoter within the aforementioned range is conducive to obtaining a better depolymerization effect.

[0047] In the present invention, the nylon may be molten nylon.

[0048] In the present invention, the microwave reactor is preferably a continuous flow reactor. The present invention can use microwaves as the only heating source. The material of the microwave reactor can be a material that is transparent to microwaves, such as polytetrafluoroethylene or Si3N4.

[0049] In the present invention, the microwave frequency may be 915±25 MHz or 2450±25 MHz, more preferably 2450 MHz. The present invention has found that using microwaves of the above frequencies, especially 2450 MHz, can achieve better depolymerization effects.

[0050] In the present invention, the temperature of the depolymerization reaction can be 150-300°C, preferably 180-250°C, more preferably 200-230°C, such as 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C. If the temperature is too low, the depolymerization efficiency is low, and if the temperature is too high, the reaction container is difficult to withstand the autogenous pressure. Therefore, the reaction temperature is controlled within the scope of the present invention, which is conducive to taking into account the depolymerization efficiency and the bearing conditions of the reaction container. In some embodiments, the material of the microwave reactor is polytetrafluoroethylene, and the temperature of the depolymerization reaction can be 150-230°C, such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C. In some embodiments, the material of the microwave reactor is Si3N4, and the temperature of the depolymerization reaction can be 150-300°C, such as 150°C, 200°C, 250°C, 300°C.

[0051] In the present invention, the depolymerization reaction time can be 5-240 min, preferably 10-60 min, such as 10 min, 20 min, 30 min, 40 min, 50 min, 60 min. In the present invention, controlling the depolymerization reaction time within the above preferred range can obtain a better depolymerization effect. When using a continuous flow reactor, the depolymerization reaction time is equivalent to the residence time of nylon in the continuous flow reactor.

[0052] The nylon recovery method of the present invention further comprises cooling, crystallizing and filtering the product of the depolymerization reaction in sequence, re-crystallizing and refining the solid product obtained by filtration to obtain a diacid monomer and a diacid monomer mother liquor; and adding alkali to neutralize the liquid product obtained by filtration, adding an extractant to separate and extract, and distilling to obtain hexamethylenediamine and a mixed solution.

[0053] The recrystallization purification of the present invention may sequentially include water washing before recrystallization, recrystallization, and separation and drying after recrystallization. The diacid monomer mother liquor obtained by recrystallization purification of the present invention may be put into a microwave reactor as a raw material for microwave depolymerization.

[0054] In the process of adding alkali for neutralization of the present invention, the pH end point is 10-14, preferably 11-13, for example 11, 11.5, 12, 12.5, 13. Too low pH will result in the inability to completely convert hexamethylenediamine salt into hexamethylenediamine, and too high pH will increase the operating cost. The present invention controls the pH within the above preferred range, which is conducive to increasing the output of hexamethylenediamine while reducing the production cost.

[0055] In the present invention, the extractant can be any solvent that is insoluble in water, has a greater solubility in hexamethylenediamine than water, and has a large difference in boiling point with hexamethylenediamine. Preferably, the extractant is a mixture of two or more solvents, each of which has a boiling point higher than hexamethylenediamine and poor solubility in water. More preferably, the extractant is a mixture of aromatic hydrocarbons and alcohols. In the mixture, the mass ratio of aromatic hydrocarbons to alcohols can be 1:3-3:1, preferably 1:2-2:1, such as 1:1.5, 1:1, 1.5:1. The mass ratio of aromatic hydrocarbons to alcohols within the above range is conducive to improving the yield of hexamethylenediamine. The aromatic hydrocarbons can be one or more selected from naphthalene, methylnaphthalene, dimethylnaphthalene and biphenyl. The alcohol can be one or more of n-nonanol, n-decanol and decylmethanol. In the present invention, the use of a mixture of aromatic hydrocarbons and alcohols as an extractant is conducive to improving the yield of hexamethylenediamine; further, the use of a solvent having a boiling point higher than that of hexamethylenediamine as an extractant can further improve the yield of hexamethylenediamine.

[0056] In the present invention, the mass ratio of the hydrolyzate obtained by adding alkali to the extractant can be 1:(1-5), such as 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5. A high amount of extractant is beneficial to improving the yield of hexamethylenediamine, but will increase the operating cost. The mass ratio of the hydrolyzate obtained by adding alkali to the extractant is controlled within the scope of the present application, which is beneficial to taking into account both the yield of hexamethylenediamine and the recovery cost.

[0057] In the present invention, the extraction temperature can be 40-100°C, for example 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C.

[0058] In the distillation process of the present invention, hexamethylenediamine is collected at the top of the tower, and the mixed solution containing the extractant is in the bottom of the tower. The mixed solution containing the extractant is used as the extractant for recycling.

[0059] In some embodiments, the microwave-assisted chemical recovery method of waste nylon provided by the present invention includes: microwave depolymerization, cooling crystallization, filtration, water washing, refining, neutralization, extraction, separation, and distillation. The monomer obtained after recovery can be directly used for nylon polymerization. The recovered waste nylon, the recycled diacid monomer mother liquor, the catalyst and the microwave absorption promoter are added together into a microwave depolymerization reactor for continuous depolymerization reaction. After the reaction is completed, the final product is the diacid monomer, the acid salt corresponding to hexamethylenediamine and a small amount of residual acid. The reaction product is filtered after cooling crystallization, and the filtered solid product is washed with water and then enters the refining kettle for recrystallization and refining. After separation and drying, the refined diacid monomer can be obtained, and the diacid monomer mother liquor in the refining kettle can continue to be used for microwave depolymerization; the liquid product after the depolymerization product is filtered is neutralized by adding alkali, and then the extractant is added for extraction. The aqueous phase after extraction is discharged as wastewater, and the oil phase can obtain hexamethylenediamine after distillation. The remaining extractant is continued to be used for extraction operation. The process flow of recovering nylon is as follows: Figure 1 shown.

[0060] In some embodiments, the microwave-assisted chemical recovery method of waste nylon 66 provided by the present invention comprises: microwave depolymerization, cooling crystallization, filtration, washing, refining, neutralization, extraction, separation, distillation (such as Figure 2 As shown), the monomer obtained after recovery can be directly used for nylon 66 polymerization. The recovered waste nylon 66, the recycled adipic acid mother liquor, the catalyst and the microwave absorption promoter are added together into a microwave depolymerization reactor for continuous depolymerization reaction. After the reaction, the final product is adipic acid, the acid salt corresponding to hexamethylenediamine and a small amount of residual acid. The reaction product is filtered after cooling and crystallization. The filtered solid product is washed with water and then enters the refining kettle for recrystallization and refining. After separation and drying, refined adipic acid can be obtained. The adipic acid mother liquor in the refining kettle can be further used for microwave depolymerization; the liquid product after the depolymerization product is filtered is neutralized by adding alkali, and then the extractant is added for extraction. The aqueous phase after extraction is discharged as waste water, and the oil phase can obtain hexamethylenediamine after distillation. The remaining extractant is further used for extraction operation. The process flow of recovering nylon 66 is as follows: Figure 2 Shown

[0061] Compared with the prior art, the present invention has the following beneficial technical effects:

[0062] (1) Compared with the existing hydrolysis depolymerization method, the depolymerization reaction in the present invention is carried out in a microwave reactor, which can be continuously produced. Microwave heating is used as a heat source, the reaction conditions are milder, the reaction efficiency is higher, the reaction time is short, and the product can be directly used for polymerization reaction, avoiding the problem of complex products requiring post-processing in other methods;

[0063] (2) In the subsequent separation process of the depolymerization reaction product, the present invention adopts the method of first extraction and then distillation, thereby avoiding the problems of excessive energy consumption and salt precipitation at the bottom of the distillation tower that are not suitable for continuous production in the traditional direct distillation of aqueous solution;

[0064] (3) Therefore, compared with the prior art, the present invention has the advantages of relatively mild depolymerization reaction conditions, short reaction time, simple products, and the depolymerization and separation process is suitable for continuous production.

[0065] The present invention will be described below in the form of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents and materials used in the examples are, unless otherwise stated, conventional methods, reagents and materials in the art. The raw material compounds in the examples can all be purchased through commercial routes.

[0066] Example 1

[0067] This embodiment follows Figure 1The process shown is to recycle waste nylon 66 (PA66), and the specific steps are as follows:

[0068] (1) HCl solution and microwave absorption promoter are directly injected into a continuous flow microwave reactor with a volume of 1.5 L and made of polytetrafluoroethylene (microwave frequency is 2450 MHz) through a feed pump, and waste nylon 66 particles are preheated to a molten state and then injected into the microwave reactor through a pump to perform a depolymerization reaction; wherein the concentration of the HCl solution is 30 wt% (the mass ratio of the converted pure HCl to the waste nylon 66 particles is 1:1), the microwave absorption promoter is Na3PO4, the mass of the microwave absorption promoter is 5% of the mass of the waste nylon 66 particles, and the feed space velocity of the molten nylon 66 is 6 h -1 (equivalent to a residence time of 10 min), microwaves were used as the heating source, and the temperature in the microwave reactor was 200 °C;

[0069] (2) After cooling the material obtained by the depolymerization reaction in step (1), adipic acid is precipitated in a crystalline state, filtered, and the filter cake (solid product) is washed to obtain adipic acid crude product, which is then decolorized with activated carbon and then sent to a crystallization kettle for cooling, crystallization, separation, and drying to obtain adipic acid and adipic acid mother liquor; NaOH is added to the filtered liquid product until the solution pH is 13.0, and the hexamethylenediamine hydrochloride therein is converted into hexamethylenediamine; then the hydrolyzate obtained by adding alkali and the extractant are put into an extraction kettle in a mass ratio of 1:2, wherein the extractant is a mixture of naphthalene and n-decanol in a mass ratio of 1:1, the liquid in the extraction kettle is heated to 70° C. and stirred until the oil and water phases are fully in contact, and then the stirring is stopped (the purpose is to extract as much hexamethylenediamine in the original water phase as possible into the oil phase), the material is allowed to stand and stratify, the water phase is put into a wastewater treatment process, and the oil phase is transported to a distillation tower for separation to obtain hexamethylenediamine, and the final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 90.7%.

[0070] Example 2

[0071] The other conditions of this embodiment are the same as those of Example 1, except that the reactor of this embodiment is a 1.5L Si3N4 microwave reactor, the microwave absorption promoter is NH4H2PO4 with a mass of 5% of the mass of nylon, the temperature in the microwave reactor is 250°C, and the final yield of adipic acid is 94.1%, and the yield of hexamethylenediamine is 91.0%.

[0072] Example 3

[0073] The other conditions of this embodiment are the same as those of embodiment 2, except that the microwave absorption promoter of this embodiment is NH4H2PO4 with a mass of 10% of the mass of nylon, and the feed space velocity is 12h -1 (equivalent to a residence time of 5 min), the final yield of adipic acid was 94.0%, and the yield of hexamethylenediamine was 91.2%.

[0074] It can be seen from Examples 1-3 that under the conditions of Example 1, the depolymerization is already quite thorough, and increasing the reaction temperature has little effect on the yield. However, after increasing the temperature, significantly reducing the residence time and appropriately increasing the amount of additives can still achieve a good monomer yield (see Example 3).

[0075] Example 4

[0076] The other conditions of this embodiment are the same as those of embodiment 1, except that the mass of the microwave absorption promoter in this embodiment is 2% of the mass of nylon, and the feed space velocity is 3h -1 (equivalent to a residence time of 20 min), the final yield of adipic acid was 92.5%, and the yield of hexamethylenediamine was 88.5%.

[0077] Example 5

[0078] The other conditions of this embodiment are the same as those of embodiment 4, except that the temperature in the microwave reactor of this embodiment is 230°C, the feed space velocity is 4h -1 (equivalent to a residence time of 15 min), the final yield of adipic acid was 92.5%, and the yield of hexamethylenediamine was 89.0%.

[0079] Example 6

[0080] The other conditions of this embodiment are the same as those of embodiment 4, except that the reactor of this embodiment is a 1.5L Si3N4 microwave reactor and the feed space velocity is 6h -1 (equivalent to a residence time of 10 min), the temperature in the microwave reactor was 250° C., and the final yield of adipic acid was 92.9%, and the yield of hexamethylenediamine was 90.0%.

[0081] It can be seen from this embodiment that the Si3N4 material reactor can withstand higher pressure, allow higher reaction temperature, and ensure product yield while having a higher feed space velocity.

[0082] Example 7

[0083] The other conditions of this embodiment are the same as those of Example 1, except that the catalyst of this embodiment is a 30wt% H2SO4 solution (the mass ratio of the converted pure H2SO4 to the waste nylon 66 particles is 1:1), and the final yield of adipic acid is 90.0%, and the yield of hexamethylenediamine is 87.5%.

[0084] Example 8

[0085] The other conditions of this embodiment are the same as those of embodiment 7, except that the mass ratio of the converted pure H2SO4 to the waste nylon 66 particles in this embodiment is 2:1, and the final adipic acid yield is 93.4%, and the hexamethylenediamine yield is 90.3%.

[0086] From this example, it can be seen that the monomer yield is slightly improved by adding more catalyst.

[0087] Example 9

[0088] The other conditions of this embodiment are the same as those of embodiment 1, except that the feed air velocity of this embodiment is 0.5h -1 (equivalent to a residence time of 120 min), the final yield of adipic acid was 94.0%, and the yield of hexamethylenediamine was 91.5%.

[0089] It can be seen from this example that the monomer yield is slightly improved by prolonging the reaction time.

[0090] Example 10

[0091] The other conditions of this embodiment are the same as those of embodiment 1, except that the mass ratio of the hydrolyzate obtained by adding alkali to the extractant in this embodiment is 1:4, and the final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 92.0%.

[0092] Embodiment 11

[0093] The other conditions of this embodiment are the same as those of embodiment 1, except that the mass ratio of the hydrolyzate obtained by adding alkali to the extract in this embodiment is 1:1, and the final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 85.0%.

[0094] Example 12

[0095] The other conditions of this embodiment are the same as those of embodiment 1, except that the extractant of this embodiment is a mixture of methylnaphthalene and decylmethanol in a mass ratio of 1:1, and the final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 90.0%.

[0096] Embodiment 13

[0097] The other conditions of this embodiment are the same as those of embodiment 1, except that the feed air velocity of this embodiment is 0.25h -1 (equivalent to a residence time of 240 min), the final yield of adipic acid was 94.0%, and the yield of hexamethylenediamine was 91.3%.

[0098] Embodiment 14

[0099] The other conditions of this embodiment are the same as those of embodiment 1, except that the microwave frequency of this embodiment is 915 MHz and the feed space velocity is 3 h -1 (equivalent to a residence time of 20 min), the final yield of adipic acid was 90.4%, and the yield of hexamethylenediamine was 88.1%.

[0100] Embodiment 15

[0101] The other conditions of this embodiment are the same as those of embodiment 1, except that the microwave absorption promoter of this embodiment is ZnCl2, and the final yield of adipic acid is 92.9%, and the yield of hexamethylenediamine is 90.5%.

[0102] Example 16

[0103] The other conditions of this embodiment are the same as those of embodiment 1, except that the microwave absorption promoter of this embodiment is CuSO4, and the final yield of adipic acid is 92.7%, and the yield of hexamethylenediamine is 90.0%.

[0104] Embodiment 17

[0105] The other conditions of this example are the same as those of Example 1, except that no microwave absorption promoter is added in this example, and the feed space velocity is 2h -1 (equivalent to a residence time of 30 min), the final yield of adipic acid was 92.3%, and the yield of hexamethylenediamine was 88.7%.

[0106] Embodiment 18

[0107] The other conditions of this embodiment are the same as those of embodiment 17, except that the feed space velocity of this embodiment is 3h -1 (equivalent to a residence time of 20 min), the final yield of adipic acid was 85.2%, and the yield of hexamethylenediamine was 82.8%.

[0108] Embodiment 19

[0109] The other conditions of this embodiment are the same as those of embodiment 1, except that the recycled material of this embodiment is waste nylon 610, the final yield of sebacic acid is 94.0%, and the yield of hexamethylenediamine is 90.2%.

[0110] Embodiment 20

[0111] The other conditions of this embodiment are the same as those of embodiment 1, except that the recycled material of this embodiment is waste nylon 612, the final yield of dodecanedioic acid is 94.2%, and the yield of hexamethylenediamine is 89.7%.

[0112] Embodiment 21

[0113] The other conditions of this embodiment are the same as those of embodiment 1, except that the recycled material of this embodiment is waste nylon 6T, the final yield of terephthalic acid is 93.6%, and the yield of hexamethylenediamine is 90.3%.

[0114] Comparative Example 1

[0115] The other conditions of this comparative example are the same as those of Example 1, except that the depolymerization reaction of this comparative example is carried out in an ordinary hydrothermal kettle, and an electric heating jacket is used as an external heating source, so there is no need to add a microwave absorption promoter, and the reaction is an intermittent operation. After the raw materials are added to the hydrothermal kettle, the temperature is raised to 200° C. and maintained for 10 minutes. There is almost no change in nylon, and subsequent operations cannot be carried out.

[0116] Comparative Example 2

[0117] (1) A NaOH solution and a microwave absorption promoter are directly injected into a microwave reactor with a volume of 1.5 L and a polytetrafluoroethylene liner (microwave frequency is 2450 MHz) through a feed pump, and waste nylon 66 particles are preheated to a molten state and then injected into the microwave reactor through a pump to perform a depolymerization reaction; wherein the concentration of the NaOH solution is 30 wt% (the mass ratio of the converted pure NaOH to the waste nylon 66 particles is 1:1), the microwave absorption promoter is Na3PO4, the mass of the microwave absorption promoter is 5% of the mass of the waste nylon 66 particles, and the nylon feed space velocity is 6 h -1 (residence time 10 min), the temperature in the microwave reactor was 200 °C;

[0118] (2) cooling the material obtained from the depolymerization reaction in step (1), precipitating adipic acid in a crystalline state, filtering, washing the filter cake (solid product) to obtain adipic acid crude product, decolorizing with activated carbon, and then sending it to a crystallization kettle for cooling, crystallization, separation, and drying to obtain refined adipic acid and adipic acid mother liquor;

[0119] The hydrolyzate obtained by the depolymerization reaction and the extractant are put into an extraction kettle in a mass ratio of 1:2, wherein the extractant is a mixture of naphthalene and n-decanol in a mass ratio of 1:1, the liquid in the extraction kettle is heated to 70°C and stirred until the oil and water phases are fully in contact, and then the stirring is stopped, and the material is allowed to stand and separate, and the oil phase is transported to a distillation tower for separation to obtain hexamethylenediamine, and HCl solution is added to the aqueous phase until the solution pH is 2.8, and the adipic acid salt therein is converted into adipic acid, and then activated carbon is used for decolorization, and then the mixture is sent to a crystallization kettle for cooling, crystallization, separation, and drying to obtain adipic acid, with a final adipic acid yield of 85.5% and a hexamethylenediamine yield of 91.2%.

[0120] In this comparative example, alkaline depolymerization, extraction and separation are first performed to obtain hexamethylenediamine, and then acidification, precipitation and filtration are performed to obtain adipic acid. The yield of adipic acid in this process flow is relatively low.

[0121] Comparative Example 3

[0122] The other conditions of this comparative example are the same as those of Example 1, except that the mass ratio of the converted pure HCl to the waste nylon 66 particles in this comparative example is 1:4, and the final yield of adipic acid is 25.7%, and the yield of hexamethylenediamine is 23.2%.

[0123] Comparative Example 4

[0124] The other conditions of this comparative example are the same as those of Example 8, except that the mass ratio of the converted pure H2SO4 to the waste nylon 66 particles in this comparative example is 1:4, and the final yield of adipic acid is 32.0%, and the yield of hexamethylenediamine is 30.9%.

[0125] Comparative Examples 3-4 show that lower catalyst dosage will lead to incomplete depolymerization.

[0126] Comparative Example 5

[0127] The other conditions of this comparative example are the same as those of Example 1, except that the temperature in the microwave reactor of this comparative example is 140° C., and a large amount of undepolymerized nylon exists in the material after the reaction, so subsequent operations cannot be performed.

[0128] Comparative Example 6

[0129] The other conditions of this comparative example are the same as those of Example 1, except that the feed space velocity of this comparative example is 20h -1 (equivalent to a residence time of 3 min), a large amount of undepolymerized nylon exists in the material after the reaction, and subsequent operations cannot be carried out.

[0130] Comparative Example 7

[0131] The other conditions of this comparative example are the same as those of Example 1, except that NaOH is added to the solution until the pH value is 9.0. The final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 57.9%.

[0132] Comparative Example 8

[0133] The other conditions of this comparative example are the same as those of Example 1, except that the extractant of this comparative example is n-decanol, and the final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 75.3%.

[0134] Comparative Example 9

[0135] The other conditions of this comparative example are the same as those of Example 1, except that the extractant of this comparative example is a mixture of benzene and n-butanol in a mass ratio of 1:1. The final yield of adipic acid is 93.3%, and the yield of hexamethylenediamine is 80.8%.

[0136] The extractants in Comparative Example 9 are benzene and n-butanol, whose boiling points are lower than hexamethylenediamine. The extractants in Example 1 are naphthalene and n-decanol, whose boiling points are higher than hexamethylenediamine. It can be seen from Example 1 and Comparative Example 9 that the use of an extractant with a boiling point higher than hexamethylenediamine is beneficial to increasing the yield of hexamethylenediamine.

Claims

1. A method for recycling nylon, characterized in that: The method comprises microwave depolymerization, which comprises adding nylon, a catalyst and an optionally added microwave absorption promoter into a microwave reactor to carry out a depolymerization reaction.

2. The recycling method according to claim 1, characterized in that: The recovery method has one or more of the following characteristics: The catalyst is an acid, and the acid is preferably selected from one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid; The mass of the catalyst is 40%-300% of the mass of nylon, preferably 50%-100%; The microwave absorption promoter is selected from one or more of Na3PO4, NH4H2PO4, ZnCl2 and CuSO4; The mass of the microwave absorption promoter is 0-10% of the mass of nylon; The material of the microwave reactor is polytetrafluoroethylene and / or Si3N4; Microwave frequency is 915±25MHz or 2450±25MHz; The temperature of the depolymerization reaction is 150-300°C, preferably 180-250°C, more preferably 200-230°C; The depolymerization reaction time is ≥5 min, preferably 5-240 min, more preferably 10-60 min; The nylon is selected from one or more of nylon 66, nylon 610, nylon 612 and nylon 6T.

3. The recycling method according to claim 2, characterized in that: The material of the microwave reactor is polytetrafluoroethylene, and the temperature of the depolymerization reaction is 150-230°C; or The material of the microwave reactor is Si3N4, and the temperature of the depolymerization reaction is 150-300°C.

4. The recycling method according to claim 1, characterized in that: The nylon is molten nylon.

5. The recycling method according to claim 1, characterized in that: The recovery method further comprises sequentially cooling, crystallizing and filtering the product of the depolymerization reaction, and refining the solid product obtained by filtration by recrystallization to obtain a diacid monomer and a diacid monomer mother liquor; sequentially neutralizing the liquid product obtained by filtration by adding alkali, extracting and separating by adding an extractant, and distilling to obtain hexamethylenediamine and a mixed solution; The diacid monomer is preferably selected from one or more of adipic acid, sebacic acid, dodecanedioic acid and terephthalic acid.

6. The recycling method according to claim 5, characterized in that: The recrystallization purification includes water washing before recrystallization, recrystallization, and separation and drying after recrystallization.

7. The recycling method according to claim 5, characterized in that: During the process of adding alkali for neutralization, the pH end point is 10-14, preferably 11-13.

8. The recycling method according to claim 5, characterized in that: The recovery method has one or more of the following characteristics: The extractant is a mixture of aromatic hydrocarbons and alcohols; The mass ratio of the hydrolyzate obtained by adding alkali to the extractant is 1:(1-5); The temperature of the extraction separation is 40-100°C.

9. The recycling method according to claim 5, characterized in that: The recovery method further comprises using the diacid monomer mother liquor as a raw material for the microwave depolymerization.

10. The recycling method according to claim 5, characterized in that: The recovery method further comprises using the mixed solution as an extractant.

Images