CN117756690A - Efficient catalytic hydrolysis recycling method for polyamide 6 - Google Patents
Efficient catalytic hydrolysis recycling method for polyamide 6 Download PDFInfo
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- CN117756690A CN117756690A CN202311763812.7A CN202311763812A CN117756690A CN 117756690 A CN117756690 A CN 117756690A CN 202311763812 A CN202311763812 A CN 202311763812A CN 117756690 A CN117756690 A CN 117756690A
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- polyamide
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- caprolactam
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- 238000001125 extrusion Methods 0.000 claims description 21
- 239000003795 chemical substances by application Substances 0.000 claims description 17
- 238000006116 polymerization reaction Methods 0.000 claims description 16
- 239000002253 acid Substances 0.000 claims description 15
- 239000000243 solution Substances 0.000 claims description 15
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- 238000006243 chemical reaction Methods 0.000 claims description 13
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- VILAVOFMIJHSJA-UHFFFAOYSA-N dicarbon monoxide Chemical compound [C]=C=O VILAVOFMIJHSJA-UHFFFAOYSA-N 0.000 claims description 8
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 claims description 8
- 125000002915 carbonyl group Chemical group [*:2]C([*:1])=O 0.000 claims description 5
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims description 4
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims description 4
- 239000011592 zinc chloride Substances 0.000 claims description 4
- 235000005074 zinc chloride Nutrition 0.000 claims description 4
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 claims description 3
- ZOIORXHNWRGPMV-UHFFFAOYSA-N acetic acid;zinc Chemical compound [Zn].CC(O)=O.CC(O)=O ZOIORXHNWRGPMV-UHFFFAOYSA-N 0.000 claims description 3
- 239000001632 sodium acetate Substances 0.000 claims description 3
- 235000017281 sodium acetate Nutrition 0.000 claims description 3
- 239000004246 zinc acetate Substances 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 claims description 2
- 239000000463 material Substances 0.000 claims 1
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- 238000001704 evaporation Methods 0.000 description 13
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- KKEYFWRCBNTPAC-UHFFFAOYSA-N Terephthalic acid Chemical compound OC(=O)C1=CC=C(C(O)=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-N 0.000 description 8
- WNLRTRBMVRJNCN-UHFFFAOYSA-N adipic acid Chemical compound OC(=O)CCCCC(O)=O WNLRTRBMVRJNCN-UHFFFAOYSA-N 0.000 description 8
- 230000008901 benefit Effects 0.000 description 7
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- 238000006068 polycondensation reaction Methods 0.000 description 5
- 239000001361 adipic acid Substances 0.000 description 4
- 235000011037 adipic acid Nutrition 0.000 description 4
- 238000009833 condensation Methods 0.000 description 4
- 230000005494 condensation Effects 0.000 description 4
- QQVIHTHCMHWDBS-UHFFFAOYSA-N isophthalic acid Chemical compound OC(=O)C1=CC=CC(C(O)=O)=C1 QQVIHTHCMHWDBS-UHFFFAOYSA-N 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- 238000011084 recovery Methods 0.000 description 4
- 230000000269 nucleophilic effect Effects 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
- 238000010008 shearing Methods 0.000 description 3
- 238000007086 side reaction Methods 0.000 description 3
- 239000004952 Polyamide Substances 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
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- BYEAHWXPCBROCE-UHFFFAOYSA-N 1,1,1,3,3,3-hexafluoropropan-2-ol Chemical compound FC(F)(F)C(O)C(F)(F)F BYEAHWXPCBROCE-UHFFFAOYSA-N 0.000 description 1
- SLXKOJJOQWFEFD-UHFFFAOYSA-N 6-aminohexanoic acid Chemical compound NCCCCCC(O)=O SLXKOJJOQWFEFD-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/62—Plastics recycling; Rubber recycling
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- Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
Abstract
The invention relates to a method for recycling polyamide 6 through high-efficiency catalytic hydrolysis, which comprises the steps of pre-depolymerizing waste polyamide 6 in a screw under the action of a depolymerization catalyst to obtain a pre-depolymerized substance, hydrolyzing the pre-depolymerized substance in a hydrolysis kettle under the action of the depolymerization catalyst, discharging water vapor from the top of the hydrolysis kettle after hydrolysis, condensing and collecting to obtain a caprolactam water solution, and performing post-treatment (concentration and purification) to obtain caprolactam. The method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 has higher efficiency, and can be widely applied to the field of recycling and reutilizing waste plastics and fibers.
Description
Technical Field
The invention belongs to the technical field of waste polyamide recovery, and relates to a method for recycling polyamide 6 through efficient catalytic hydrolysis.
Background
Polyamide 6 is one of the most excellent varieties of the polyamide family, and is widely used in engineering plastics and fiber textile fields due to its advantages of high strength and toughness, abrasion resistance, moisture absorption, easy dyeing, etc. The good chemical stability of the polyamide 6 brings excellent application performance, and at the same time, the polyamide 6 is difficult to degrade in natural environment, the existing treatment method for the waste polyamide 6 is mainly landfilled or burnt, only a small amount of the polyamide 6 is recycled (mainly physically recycled), and the ecological environment pollution and the resource waste are caused.
The recycling method of polyamide 6 is divided into a physical method and a chemical method; most of the physical methods adopt screw melting extrusion for reuse, the method has less equipment investment and simple and easy processing process, but the process is carried out under the action of heat and shearing force under the aerobic condition, and the breakage of molecular chains and other side reactions are inevitably caused, so that the performance of the regenerated polyamide 6 is reduced, and new waste is caused after a short period of time; chemical processes, in particular hydrolysis processes, are limited by the high reaction conditions and recovery costs and have not yet been applied on a large scale, but have an incomparable advantage in achieving a closed loop recovery route for the waste polyamide 6.
The patent CN101423487A discloses a method for catalyzing waste nylon 6 to degrade and recycle epsilon-caprolactam, which takes water as a reaction medium, takes phosphotungstic heteropolyacid as a catalyst, and carries out reaction for 0.5-3 hours at 280-330 ℃, and then carries out alkali liquor neutralization, organic solvent extraction, deionized water cleaning and dehydration drying to obtain caprolactam solid with the yield of 70-81 percent.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a method for efficiently catalyzing hydrolysis and recycling of polyamide 6.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the steps of pre-depolymerizing waste polyamide 6 in a screw under the action of a depolymerization catalyst to obtain a pre-depolymerized substance, hydrolyzing the pre-depolymerized substance in a hydrolysis kettle under the action of the depolymerization catalyst, discharging water vapor from the top of the hydrolysis kettle after hydrolysis, condensing and collecting to obtain a caprolactam aqueous solution, and performing post-treatment (concentration and purification) to obtain caprolactam; the hydrolysis process of the waste polyamide 6 is divided into two stages, wherein the first stage is that macromolecular chains are hydrolyzed into pre-depolymerized substances, the second stage is that the pre-depolymerized substances are hydrolyzed into caprolactam, caprolactam is mainly generated in the second stage, and the first stage is that the breaking of the macromolecular chains of the polyamide 6 is difficult if the breaking of the macromolecular chains of the polyamide 6 is realized only by means of hydrolysis, so that the breaking of the macromolecular chains of the polyamide 6 is realized under the action of a depolymerization catalyst by utilizing the heat and shearing action of a screw rod, and the purposes of melting the polyamide 6 and conveying the melt into a hydrolysis kettle are achieved, so that the pre-depolymerized substance melt and superheated steam can form a larger contact area more quickly, and the hydrolysis difficulty is reduced.
As a preferable technical scheme:
the method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 has the advantages that the relative viscosity of the pre-depolymerization is less than or equal to 1.6, the relative viscosity of the pre-depolymerization is low, the flow is easy, the interface update is quick, the contact with water vapor is facilitated, and meanwhile, under the relative viscosity, the hydrolysis process can directly enter a process of generating a large amount of caprolactam, so that the hydrolysis process is facilitated to be accelerated.
The method for recycling the polyamide 6 through high-efficiency catalytic hydrolysis comprises the following specific processes: feeding waste polyamide 6 and depolymerization master batch into a screw for melt extrusion to obtain a pre-depolymerized substance, and then conveying the pre-depolymerized substance into a hydrolysis kettle for hydrolysis to obtain a caprolactam water solution, and performing post-treatment to obtain caprolactam, wherein the depolymerization master batch comprises polyamide 6 and the depolymerization catalyst dispersed therein; the invention adds the depolymerization catalyst into the screw together with the waste polyamide 6 in the form of depolymerization master batch, instead of directly adding the depolymerization catalyst into the screw together with the waste polyamide 6, because the depolymerization catalyst is in a powder form, the waste polyamide 6 is in a fiber form, a block form or a particle form, if the depolymerization catalyst is directly added into the screw together with the waste polyamide 6, the depolymerization catalyst and the waste polyamide 6 are unevenly mixed, and in addition, the depolymerization catalyst absorbs water, and the catalytic effect of the depolymerization catalyst is not affected, but metering misalignment is caused.
A process for the efficient catalytic hydrolysis recycling of polyamide 6 as described above, the depolymerization catalyst being used to form bonds with the carbonyl groups of the amide bonds to enhance the electropositivity of the carbonyl carbon.
The method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 comprises the step of preparing the depolymerization catalyst, wherein the depolymerization catalyst is one or more of zinc chloride, ferric chloride, sodium acetate and zinc acetate.
The preparation process of the depolymerized master batch by the method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 comprises the following steps: and mixing caprolactam, a dibasic acid end-capping agent, deionized water and the depolymerization catalyst, and performing polymerization reaction to obtain depolymerization master batch.
The method for recycling the polyamide 6 through high-efficiency catalytic hydrolysis is carried out at the temperature of 80-140 ℃ with stirring, and the stirring speed is 150-300 rpm; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.3-0.5 wt%, 2-3 wt% and 5-10 wt% of the addition amount of caprolactam.
The method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 comprises the following steps of: under the condition of 200-220 ℃, the reaction is carried out for 1-2 hours under the conditions of 0.1-0.6 MPa of pressure and the protection of nitrogen or inert gas, then the pressure is relieved to normal pressure, the reaction is continued for 1-2 hours, and the nitrogen or inert gas is purged during the system purging; the polymerization reaction is carried out with stirring, and the stirring speed is 150-300 rpm.
In the polymerization reaction process, the process before decompression belongs to an open loop process, the process after decompression belongs to a polycondensation process, and the polycondensation process takes away the generated moisture through nitrogen or inert gas purging so as to promote the reaction to proceed in the direction of generating the polymer;
the purpose of preparing the depolymerization master batch is to add a depolymerization catalyst into the waste polyamide 6, so that the required depolymerization master batch does not need to be polyamide 6 with high molecular weight, and only needs to be formed by dicing, and the polymerization time is shorter than the time of the existing normal-pressure polymerization process;
since the depolymerization catalyst is used for forming bond with carbonyl of amide bond to strengthen the electropositivity of carbonyl carbon, the temperature for preparing depolymerization master batch is lower than that for preparing polyamide 6 in the prior art, and the specific principle is as follows: in the ring opening process, the main reaction process is that water molecules attack amide bonds of caprolactam to open the amide bonds to generate aminocaproic acid, and in the process, a depolymerization catalyst and a carbonyl group of the amide bonds form a bond to strengthen the electropositivity of carbonyl carbon, so that the attack of water molecules is facilitated; in the polycondensation process, the depolymerization catalyst still forms bond with the carbonyl group of the amide bond to strengthen the electropositivity of the carbonyl carbon, but the nucleophilic reagent becomes an amino-terminated group, and the addition reaction of the amino-terminated group of the polyamide 6 short chain to caprolactam and the polycondensation reaction of the amino-terminated group of the polyamide 6 short chain to the carboxyl-terminated group of the other short chain mainly occur in the polycondensation process, which is essentially nucleophilic attack of the amino-terminated group to the carbonyl carbon of the carboxyl group or the carbonyl carbon of the amide bond, and the depolymerization catalyst is used for strengthening the process.
The method for recycling the polyamide 6 through high-efficiency catalytic hydrolysis has the advantage that the diacid end capping agent is more than one of adipic acid, terephthalic acid and isophthalic acid.
The method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 has the advantages that the relative viscosity of the depolymerized master batch is 1.2-1.4, the melting point is 204-225 ℃, and the number average molecular weight is 2800-6000 g/mol; the mass ratio of the waste polyamide 6 to the depolymerized master batch is 9-100:1.
The high-efficiency catalytic hydrolysis recycling method for polyamide 6 has the advantages that the temperature of melt extrusion is 255-265 ℃, the rotating speed of a main screw is lower than 100rpm, and the current of the main screw is 5-15 Hz; the melt extrusion is performed under the protection of nitrogen or inert gas, so that the occurrence of side reactions can be reduced, and only the breakage of polyamide 6 molecular chains occurs.
In the prior researches, a screw is mostly used as a melt conveying tool or melt molding, and the phenomenon that the relative viscosity of the polyamide 6 is increased under the condition of the rest processing conditions is found that the effect of reducing the relative viscosity of the polyamide 6 can be achieved only under the specific temperature (250-265 ℃) and the main screw current (6-10 Hz). The present invention can achieve the effect of lowering the relative viscosity of polyamide 6 even if the temperature and the main screw current are different from the prior art because of adding the depolymerization catalyst.
The method for recycling the polyamide 6 through high-efficiency catalytic hydrolysis is carried out under the action of water vapor with the temperature of 220-300 ℃, the pressure of 0.6-3 MPa and the flow rate of 0.1-1 mL/min, the hydrolysis time is 30-60 min, and the caprolactam yield is more than or equal to 90%; the hydrolysis is accompanied by stirring at a stirring rate of 150-300 rpm.
The technical reaction time for hydrolysis using water vapor used in the present invention is shorter than the prior art. In the existing report of hydrolyzing polyamide 6 by using steam, the hydrolysis time is at least 180min under the condition that the caprolactam yield is more than 80 percent and is more than 270 ℃, and the hydrolysis time is only 30-60 min when the higher caprolactam yield is achieved.
The method for recycling the polyamide 6 through high-efficiency catalytic hydrolysis has the advantages that the pre-depolymerization substance flows from the top end of the hydrolysis kettle to the bottom, the input points of the water vapor are densely distributed at the bottom of the whole hydrolysis kettle, and the distribution density is high>5 pieces/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The invention controls the movement direction of the pre-depolymerization substance to be opposite to the movement direction of the water vapor during the hydrolysis, thus the contact time of the pre-depolymerization substance and the water vapor can be increased, and the hydrolysis reaction is more sufficient.
The method for efficiently catalyzing, hydrolyzing and recycling the polyamide 6 adopts three-effect evaporation for concentration, wherein the temperature ranges are 70-80 ℃, 80-100 ℃ and 100-120 ℃ respectively; the purification adopts a rectification method, wherein the temperature is 10-135 ℃ and the pressure is less than or equal to 300Pa.
Mechanism of the invention
The invention uses the screw to pre-depolymerize the waste polyamide 6 under the protection of nitrogen or inert gas, greatly reduces the occurrence of side reaction in the processing process under the anaerobic condition, and simultaneously the purpose of screw processing is to break the molecular chain of the polyamide 6, hydrolyze the polyamide 6 to caprolactam for the polymerization of regenerated polyamide 6, thereby avoiding the disadvantage of physical recovery; meanwhile, the depolymerization catalyst adopted by the invention can participate in the polymerization process of the regenerated polyamide 6, and the depolymerization catalyst does not need to be removed, so that extra steps and pollution are avoided.
The depolymerization catalyst is used for strengthening the electropositivity of carbonyl carbon through the bond formation with an amide bond, so that the nucleophilic attack of water molecules is promoted, and the purpose of hydrolyzing polyamide 6 to obtain caprolactam is achieved.
In the polymerization reaction process, in the early stage, under the action of a depolymerization catalyst, water molecules attack amide bonds of caprolactam to open the caprolactam, then the pressure is released to normal pressure, the water molecules exist in a gas form at the polymerization reaction temperature, and after being discharged along with nitrogen, a nucleophilic reagent of the polymerization reaction becomes an amino-terminated group, so that the polymerization reaction is carried out.
The hydrolysis process of polyamide 6 can be divided into two steps, firstly, the macromolecular chains of polyamide 6 are hydrolyzed to a pre-depolymerized product, and the process only generates a very small amount of water-soluble substances (caprolactam and oligomers thereof); and then hydrolyzing the pre-depolymerization product to caprolactam, wherein the relative viscosity of the pre-depolymerization product is kept unchanged basically after the reaction is finished. The depolymerization master batch and the waste polyamide 6 are conveyed to a hydrolysis kettle through a screw, and in the screw conveying process, a depolymerization catalyst in the depolymerization master batch promotes the breakage of a macromolecular chain of the polyamide 6 under the action of heat and shearing force of the screw to obtain a pre-depolymerized product; after the pre-depolymerized matter (containing the depolymerization catalyst) enters the hydrolysis kettle, the depolymerization catalyst catalyzes the hydrolysis reaction, so that the caprolactam is hydrolyzed into the caprolactam with high efficiency.
The beneficial effects are that:
(1) The method for recycling the waste polyamide 6 through the steps of pre-depolymerization, hydrolysis and post-treatment is simple, environment-friendly, high in efficiency, high in yield of caprolactam which is a final product and higher than or equal to 90%, and the quality of caprolactam is good, and the hydrolysis time only needs 30-60 min.
(2) According to the invention, the depolymerization catalyst is added into the screw together with the waste polyamide 6 in the form of depolymerization master batch by optimizing the adding mode of the depolymerization catalyst, so that the depolymerization catalyst can not only act on the hydrolysis process, but also act on the melt conveying process to achieve the effect of pre-depolymerization.
(3) The method carries out the pre-depolymerization of the waste polyamide 6 in the screw, the obtained pre-depolymerization can directly generate the reaction of caprolactam at the hydrolysis temperature, the step of breaking the polyamide 6 molecular chain at high temperature and high pressure is reduced, and the reaction process is optimized.
(4) The method controls the movement direction of the water vapor to be opposite to the movement direction of the pre-depolymerization during hydrolysis, so that the contact time of the water vapor and the pre-depolymerization can be increased, and the hydrolysis product caprolactam can be dissolved in the water vapor and condensed and collected along with the water vapor without an additional liquid-solid separation procedure.
Detailed Description
The invention is further described below in conjunction with the detailed description. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it is understood that various changes and modifications may be made by those skilled in the art after reading the teachings of the present invention, and such equivalents are intended to fall within the scope of the claims appended hereto.
The following are test methods for each performance in the examples:
relative viscosity: the measurement was carried out according to GB/T38138-2019 fiber grade polycaprolactam (PA 6) slice experiment method, 5.2 relative viscosity.
Melting point: the crystallization and melting behavior test is carried out on the sample by adopting a TA-Q20 differential scanning calorimeter, and the melting temperature and the crystallization temperature of the 5mg dry sample can be obtained by heating and cooling the sample at the speed of 10 ℃/min under the nitrogen atmosphere.
Number average molecular weight: the number average molecular weight of the samples was measured using GPC-50 type gel permeation chromatography (PL) from UK, equipped with a differential refractive index detector and a PL gel column (5 μm mixed-C), with 1, 3-hexafluoro-2-propanol as eluent at a flow rate of 1mL/min; the sample was dried and dissolved in hexafluoroisopropanol to prepare a 1.0mg/mL solution, and the column temperature was measured at 40.+ -. 1 ℃.
Yield: caprolactam yield (%) =caprolactam mass obtained by hydrolysis/waste polyamide 6 mass×100%.
Example 1
A method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the following steps:
(1) Preparing raw materials;
caprolactam;
diacid blocking agent: adipic acid;
deionized water;
depolymerization catalyst: zinc chloride;
waste polyamide 6: the number average molecular weight is 16000g/mol, and the relative viscosity is 2.2;
nitrogen or inert gas;
(2) Preparing depolymerized master batches;
mixing caprolactam, a dibasic acid end-capping agent, deionized water and a depolymerization catalyst at the temperature of 80 ℃ and the stirring speed of 150rpm, then reacting at the stirring speed of 150rpm for 1h under the conditions of the temperature of 200 ℃ and the protection of 0.1MPa, nitrogen or inert gas, releasing pressure to normal pressure, and then continuously reacting at the stirring speed of 150rpm for 1h, and purging nitrogen or inert gas by a system to obtain depolymerization master batch; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.3wt%, 2wt% and 5wt% of the addition amount of caprolactam;
the relative viscosity of the prepared depolymerized master batch is 1.2, the melting point is 204 ℃, and the number average molecular weight is 2800g/mol;
(3) Feeding waste polyamide 6 and depolymerized master batch obtained in the step (2) into a screw together according to the mass ratio of 100:1, and carrying out melt extrusion under the protection of nitrogen or inert gas to obtain a pre-depolymerized product; wherein the temperature of the melt extrusion is 255 ℃, the rotation speed of the main screw is 95rpm, and the current of the main screw is 15Hz;
the relative viscosity of the obtained pre-depolymerized product was 1.6;
(4) Flowing the pre-depolymerized product obtained in the step (3) from the top end of the hydrolysis kettle to the bottom, wherein the input point of water vapor is 9 pieces/cm 3 Is distributed in the density ofHydrolyzing the bottom of the whole hydrolysis kettle for 30min at a stirring speed of 150rpm under the action of water vapor with the temperature of 220 ℃ and the pressure of 0.6MPa and the flow rate of 0.1mL/min, discharging the water vapor from the top of the hydrolysis kettle after hydrolysis, and condensing and collecting to obtain a caprolactam water solution;
(5) Treating the caprolactam water solution obtained in the step (4) by adopting triple effect evaporation, and then treating by adopting a rectification method under the conditions of the temperature of 100 ℃ and the pressure of 300Pa to obtain caprolactam; wherein the temperature of the triple effect evaporation is 70 ℃, 80 ℃ and 100 ℃ respectively.
The final caprolactam is produced in a yield of 90%.
Comparative example 1
A process for the efficient catalytic hydrolysis recycling of polyamide 6, substantially identical to example 1, except that: without step (2), only the waste polyamide 6 is fed into a screw for melt extrusion in step (3) to obtain a melt, and the melt obtained in step (3) is conveyed into a hydrolysis kettle together with a depolymerization catalyst (the type and the quality are the same as those in example 1) in step (4).
The final caprolactam is produced in a yield of 70%.
As can be seen from comparison between comparative example 1 and example 1, the comparative example 1 does not perform pre-depolymerization, which results in smaller contact area between the melt and the steam, poorer hydrolysis effect and lower yield, because the waste polyamide 6 is still in a longer state when entering the hydrolysis kettle after being melted by the screw, and macroscopically shows that the melt viscosity is large, which causes that the melt enters the hydrolysis kettle from the screw discharge port to contact with the steam in a more stable manner, the steam is difficult to contact with the molecular chain inside the melt, and the steam is unfavorable to overflow after the melt contacts the bottom of the hydrolysis kettle, so that the hydrolysis effect is poorer.
Comparative example 2
A process for the efficient catalytic hydrolysis recycling of polyamide 6, substantially identical to example 1, except that: without step (2), only the waste polyamide 6 is fed into a screw for melt extrusion in step (3) to obtain a melt, and the melt obtained in step (3) and a depolymerization catalyst (the type and the quality are the same as those in example 1) are conveyed into a hydrolysis kettle in step (4), wherein the hydrolysis temperature is 280 ℃, and the hydrolysis time is 4 hours.
The final caprolactam is produced in a yield of 90%.
As can be seen from comparing comparative example 2 with example 1, since comparative example 2 is not pre-depolymerized, in order to achieve the same hydrolysis effect and yield as in example 1, the hydrolysis process needs to be provided with a higher energy supply efficiency at a higher temperature while the reaction proceeds more fully for a prolonged period of time, because more energy is required to be provided for the hydrolysis process to break polyamide 6 into pre-depolymerized which is then broken to form caprolactam.
Example 2
A method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the following steps:
(1) Preparing raw materials;
caprolactam;
diacid blocking agent: terephthalic acid;
deionized water;
depolymerization catalyst: ferric chloride;
waste polyamide 6: the number average molecular weight is 16000g/mol, and the relative viscosity is 2.2;
nitrogen or inert gas;
(2) Preparing depolymerized master batches;
mixing caprolactam, a dibasic acid end-capping agent, deionized water and a depolymerization catalyst at the temperature of 100 ℃ and the stirring speed of 180rpm, then reacting at the stirring speed of 180rpm for 1h under the conditions of the temperature of 205 ℃ and the protection of 0.2MPa, nitrogen or inert gas, releasing pressure to normal pressure, and then continuously reacting at the stirring speed of 180rpm for 1h, and purging nitrogen or inert gas by a system to obtain depolymerization master batch; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.3wt%, 2wt% and 6wt% of the addition amount of caprolactam;
the relative viscosity of the prepared depolymerized master batch is 1.2, the melting point is 206 ℃, and the number average molecular weight is 3500g/mol;
(3) Feeding waste polyamide 6 and depolymerized master batch obtained in the step (2) into a screw together according to the mass ratio of 60.6:1, and carrying out melt extrusion under the protection of nitrogen or inert gas to obtain a pre-depolymerized product; wherein the temperature of the melt extrusion is 257 ℃, the rotation speed of the main screw is 90rpm, and the current of the main screw is 13Hz;
the relative viscosity of the obtained pre-depolymerized product was 1.5;
(4) Flowing the pre-depolymerized product obtained in the step (3) from the top end of the hydrolysis kettle to the bottom, wherein the input point of water vapor is 9 pieces/cm 3 The density of (2) is distributed at the bottom of the whole hydrolysis kettle, the hydrolysis is carried out for 35min under the action of water vapor with the temperature of 240 ℃ and the pressure of 1.2MPa and the flow rate of 0.2mL/min at the stirring speed of 180rpm, the water vapor is discharged from the top of the hydrolysis kettle after the hydrolysis, and the caprolactam water solution is obtained through condensation and collection;
(5) Treating the caprolactam water solution obtained in the step (4) by adopting triple effect evaporation, and then treating by adopting a rectification method under the conditions of 110 ℃ and 250Pa of pressure to obtain caprolactam; wherein the temperature of the triple effect evaporation is 70 ℃, 80 ℃ and 100 ℃ respectively.
The final caprolactam was produced in a yield of 91%.
Example 3
A method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the following steps:
(1) Preparing raw materials;
caprolactam;
diacid blocking agent: isophthalic acid;
deionized water;
depolymerization catalyst: sodium chloride;
waste polyamide 6: the number average molecular weight is 16000g/mol, and the relative viscosity is 2.2;
nitrogen or inert gas;
(2) Preparing depolymerized master batches;
mixing caprolactam, a dibasic acid end-capping agent, deionized water and a depolymerization catalyst at the temperature of 110 ℃ at the stirring rate of 210rpm, reacting at the stirring rate of 210rpm for 1.5 hours under the conditions of the temperature of 210 ℃ and the protection of 0.3MPa, nitrogen or inert gas, decompressing to normal pressure, continuing to react at the stirring rate of 210rpm for 1.5 hours, and purging nitrogen or inert gas by the system to obtain depolymerized master batch; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.4wt%, 2.5wt% and 7wt% of the addition amount of caprolactam;
the relative viscosity of the prepared depolymerized master batch is 1.4, the melting point is 220 ℃, and the number average molecular weight is 5000g/mol;
(3) Feeding waste polyamide 6 and depolymerized master batch obtained in the step (2) into a screw together according to the mass ratio of 23.3:1, and carrying out melt extrusion under the protection of nitrogen or inert gas to obtain a pre-depolymerized product; wherein the temperature of the melt extrusion is 259 ℃, the rotation speed of the main screw is 80rpm, and the current of the main screw is 10Hz;
the relative viscosity of the obtained pre-depolymerized product was 1.4;
(4) Flowing the pre-depolymerized product obtained in the step (3) from the top end of the hydrolysis kettle to the bottom, wherein the water vapor input point is 16 pieces/cm 3 The density of (2) is distributed at the bottom of the whole hydrolysis kettle, the hydrolysis is carried out for 40min at the stirring speed of 210rpm under the action of water vapor with the temperature of 260 ℃ and the pressure of 1.8MPa and the flow rate of 0.4mL/min, the water vapor is discharged from the top of the hydrolysis kettle after the hydrolysis, and the caprolactam water solution is obtained through condensation and collection;
(5) Treating the caprolactam water solution obtained in the step (4) by adopting triple effect evaporation, and then treating by adopting a rectification method under the conditions of 115 ℃ and 200Pa of pressure to obtain caprolactam; wherein the temperature of the triple effect evaporation is 75 ℃, 90 ℃ and 110 ℃ respectively.
The final caprolactam was produced in 92% yield.
Example 4
A method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the following steps:
(1) Preparing raw materials;
caprolactam;
diacid blocking agent: terephthalic acid;
deionized water;
depolymerization catalyst: sodium acetate;
waste polyamide 6: the number average molecular weight is 16000g/mol, and the relative viscosity is 2.2;
nitrogen or inert gas;
(2) Preparing depolymerized master batches;
mixing caprolactam, a dibasic acid end-capping agent, deionized water and a depolymerization catalyst at the temperature of 120 ℃ at the stirring rate of 240rpm, reacting at the stirring rate of 240rpm for 1.5 hours under the conditions of the temperature of 215 ℃ and the protection of 0.4MPa, nitrogen or inert gas, decompressing to normal pressure, continuing to react at the stirring rate of 240rpm for 1.5 hours, and purging nitrogen or inert gas by the system to obtain depolymerized master batch; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.4wt%, 2.5wt% and 8wt% of the addition amount of caprolactam;
the relative viscosity of the prepared depolymerized master batch is 1.3, the melting point is 210 ℃, and the number average molecular weight is 4000g/mol;
(3) Feeding the waste polyamide 6 and the depolymerized master batch obtained in the step (2) into a screw together according to the mass ratio of 16:1, and carrying out melt extrusion under the protection of nitrogen or inert gas to obtain a pre-depolymerized product; wherein the temperature of the melt extrusion is 261 ℃, the rotation speed of the main screw is 70rpm, and the current of the main screw is 8Hz;
the relative viscosity of the obtained pre-depolymerized product was 1.3;
(4) Flowing the pre-depolymerized product obtained in the step (3) from the top end of the hydrolysis kettle to the bottom, wherein the water vapor input point is 16 pieces/cm 3 The density of (2) is distributed at the bottom of the whole hydrolysis kettle, the hydrolysis is carried out for 45min under the action of water vapor with the temperature of 280 ℃, the pressure of 2.6MPa and the flow rate of 0.6mL/min at the stirring speed of 240rpm, the water vapor is discharged from the top of the hydrolysis kettle after the hydrolysis, and the caprolactam water solution is obtained through condensation and collection;
(5) Treating the caprolactam water solution obtained in the step (4) by adopting triple effect evaporation, and then treating by adopting a rectification method under the conditions of 120 ℃ and 150Pa of pressure to obtain caprolactam; wherein the temperature of the triple effect evaporation is 75 ℃, 90 ℃ and 110 ℃ respectively.
The final caprolactam was produced in 93% yield.
Example 5
A method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the following steps:
(1) Preparing raw materials;
caprolactam;
diacid blocking agent: adipic acid;
deionized water;
depolymerization catalyst: zinc acetate;
waste polyamide 6: the number average molecular weight is 16000g/mol, and the relative viscosity is 2.2;
nitrogen or inert gas;
(2) Preparing depolymerized master batches;
mixing caprolactam, a dibasic acid end-capping agent, deionized water and a depolymerization catalyst at the temperature of 130 ℃ and the stirring speed of 260rpm, then reacting at the stirring speed of 260rpm for 2 hours under the condition of 220 ℃ and the protection of 0.5MPa, nitrogen or inert gas, releasing pressure to normal pressure, continuing to react at the stirring speed of 260rpm for 2 hours, and purging nitrogen or inert gas by a system to obtain depolymerization master batch; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.5wt%, 3wt% and 9wt% of the addition amount of caprolactam;
the relative viscosity of the prepared depolymerized master batch is 1.3, the melting point is 225 ℃, and the number average molecular weight is 6000g/mol;
(3) Feeding the waste polyamide 6 and the depolymerized master batch obtained in the step (2) into a screw together according to the mass ratio of 9:1, and carrying out melt extrusion under the protection of nitrogen or inert gas to obtain a pre-depolymerized product; wherein the temperature of the melt extrusion is 263 ℃, the rotation speed of the main screw is 60rpm, and the current of the main screw is 6Hz;
the relative viscosity of the obtained pre-depolymerized product was 1.2;
(4) Flowing the pre-depolymerized product obtained in the step (3) from the top end of the hydrolysis kettle to the bottom, wherein the water vapor input point is 25 pieces/cm 3 The density of (C) is distributed at the bottom of the whole hydrolysis kettle under the action of water vapor with the temperature of 300 ℃, the pressure of 3MPa and the flow rate of 0.8mL/minHydrolyzing for 50min at a stirring speed of 260rpm, discharging water vapor from the top of the hydrolysis kettle after hydrolysis, and condensing and collecting to obtain caprolactam water solution;
(5) Treating the caprolactam water solution obtained in the step (4) by adopting triple effect evaporation, and then treating by adopting a rectification method under the conditions of the temperature of 130 ℃ and the pressure of 100Pa to obtain caprolactam; wherein the temperature of the triple effect evaporation is 80 ℃, 100 ℃ and 120 ℃ respectively.
The final caprolactam yield was 94%.
Example 6
A method for recycling polyamide 6 through high-efficiency catalytic hydrolysis comprises the following steps:
(1) Preparing raw materials;
caprolactam;
diacid blocking agent: a mixture of adipic acid and terephthalic acid in a mass ratio of 1:1;
deionized water;
depolymerization catalyst: a mixture of zinc chloride and ferric chloride in a mass ratio of 1:1;
waste polyamide 6: the number average molecular weight is 16000g/mol, and the relative viscosity is 2.2;
nitrogen or inert gas;
(2) Preparing depolymerized master batches;
mixing caprolactam, a dibasic acid end-capping agent, deionized water and a depolymerization catalyst at the stirring speed of 300rpm under the condition of 140 ℃, then reacting for 2 hours at the stirring speed of 300rpm under the condition of 220 ℃ under the protection of 0.6MPa, nitrogen or inert gas, releasing pressure to normal pressure, then continuing to react for 2 hours at the stirring speed of 300rpm, and purging nitrogen or inert gas by a system to obtain depolymerized master batches; the addition amounts of the dibasic acid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.5wt%, 3wt% and 10wt% of the addition amount of caprolactam;
the relative viscosity of the prepared depolymerized master batch is 1.3, the melting point is 223 ℃, and the number average molecular weight is 5500g/mol;
(3) Feeding waste polyamide 6 and depolymerized master batch obtained in the step (2) into a screw together according to the mass ratio of 10:1, and carrying out melt extrusion under the protection of nitrogen or inert gas to obtain a pre-depolymerized product; wherein the temperature of melt extrusion is 265 ℃, the rotating speed of a main screw is 50rpm, and the current of the main screw is 5Hz;
the relative viscosity of the obtained pre-depolymerized product was 1.1;
(4) Flowing the pre-depolymerized product obtained in the step (3) from the top end of the hydrolysis kettle to the bottom, wherein the water vapor input point is 25 pieces/cm 3 The density of (2) is distributed at the bottom of the whole hydrolysis kettle, the hydrolysis is carried out for 60min under the action of water vapor with the temperature of 300 ℃, the pressure of 3MPa and the flow rate of 1mL/min at the stirring speed of 300rpm, the water vapor is discharged from the top of the hydrolysis kettle after the hydrolysis, and the caprolactam water solution is obtained through condensation and collection;
(5) Treating the caprolactam water solution obtained in the step (4) by adopting triple effect evaporation, and then treating by adopting a rectification method under the conditions of the temperature of 135 ℃ and the pressure of 60Pa to obtain caprolactam; wherein the temperature of the triple effect evaporation is 80 ℃, 100 ℃ and 120 ℃ respectively.
The final caprolactam yield was 96%.
Example 7
A process for the efficient catalytic hydrolysis recycling of polyamide 6, substantially identical to example 6, except that: the depolymerization catalyst is replaced with KCl of equal mass;
the relative viscosity of the depolymerized master batch prepared in the step (2) is 1.0, the melting point is 190 ℃, and the number average molecular weight is 1500g/mol;
the relative viscosity of the prepolymer obtained in the step (3) was 2.5.
The final caprolactam yield was 60%.
Comparing example 7 with example 6, it is known that, since the depolymerization catalyst used in example 7 is KCl, under the same masterbatch polymerization conditions, the depolymerization masterbatch prepared in example 7 has a lower number average molecular weight and a lower relative viscosity, which makes it difficult to process the polymer into masterbatch with a uniform morphology, which is unfavorable for the masterbatch to be uniformly mixed with the waste polyamide 6, because KCl cannot promote polymerization by acting with an amide bond, a polymer with a higher molecular weight cannot be obtained in the same time, and at the same time, the waste polyamide 6 cannot achieve the purpose of reducing the melt viscosity entering the hydrolysis kettle in the pre-depolymerization process, because the waste polyamide 6 undergoes a repolymerization reaction after breaking under the action of heat and shear, and meanwhile, the nucleophilic attack of auxiliary water molecules cannot be performed in the hydrolysis kettle, which results in a reduction in hydrolysis efficiency.
Claims (10)
1. A method for efficiently catalyzing hydrolysis and recycling of polyamide 6 is characterized in that waste polyamide 6 is pre-depolymerized in a screw under the action of a depolymerization catalyst to obtain a pre-depolymerized substance, and the pre-depolymerized substance is hydrolyzed in a hydrolysis kettle under the action of the depolymerization catalyst to obtain a caprolactam aqueous solution, and caprolactam is obtained through post-treatment.
2. The method for high-efficiency catalytic hydrolysis and reutilization of polyamide 6 according to claim 1, wherein the relative viscosity of the pre-depolymerized product is less than or equal to 1.6.
3. The method for high-efficiency catalytic hydrolysis and reutilization of polyamide 6 according to claim 1, wherein the specific process is as follows: feeding waste polyamide 6 and depolymerization master batch into a screw for melt extrusion to obtain a pre-depolymerized product, and then conveying the pre-depolymerized product into a hydrolysis kettle for hydrolysis to obtain a caprolactam water solution and performing post-treatment to obtain caprolactam, wherein the depolymerization master batch comprises polyamide 6 and the depolymerization catalyst dispersed therein.
4. A method for efficient catalytic hydrolytic recycling of polyamide 6 as set forth in claim 3 where the depolymerization catalyst is used to bond with the carbonyl groups of amide bonds to enhance the electropositivity of the carbonyl carbon.
5. The method for efficient catalytic hydrolysis and reuse of polyamide 6 as claimed in claim 4, wherein said depolymerization catalyst is one or more of zinc chloride, ferric chloride, sodium acetate and zinc acetate.
6. The method for high-efficiency catalytic hydrolysis and recycling of polyamide 6 as recited in claim 4, wherein the preparation process of the depolymerized master batch is as follows: mixing caprolactam, a dibasic acid end-capping agent, deionized water and the depolymerization catalyst, and performing polymerization reaction to obtain depolymerized master batches;
mixing is carried out at 80-140 ℃, and the stirring speed is 150-300 rpm when the mixing is carried out; the addition amounts of the diacid end capping agent, the deionized water and the depolymerization catalyst are respectively 0.3-0.5 wt%, 2-3 wt% and 5-10 wt% of the addition amount of caprolactam;
the polymerization reaction comprises the following steps: under the condition of 200-220 ℃, the reaction is carried out for 1-2 hours under the conditions of 0.1-0.6 MPa of pressure and the protection of nitrogen or inert gas, then the pressure is relieved to normal pressure, the reaction is continued for 1-2 hours, and the nitrogen or inert gas is purged during the system purging; the polymerization reaction is carried out with stirring, and the stirring speed is 150-300 rpm.
7. The method for recycling the high-efficiency catalytic hydrolysis of the polyamide 6, which is characterized in that the relative viscosity of the depolymerized master batch is 1.2-1.4, the melting point is 204-225 ℃, and the number average molecular weight is 2800-6000 g/mol; the mass ratio of the waste polyamide 6 to the depolymerized master batch is 9-100:1.
8. A method for efficient catalytic hydrolysis and reuse of polyamide 6 according to claim 3, characterized in that the temperature of melt extrusion is 255-265 ℃, the main screw speed is lower than 100rpm, and the main screw current is 5-15 Hz; melt extrusion is performed under nitrogen or inert gas.
9. The method for recycling the high-efficiency catalytic hydrolysis of the polyamide 6 according to claim 3, wherein the hydrolysis is carried out under the action of water vapor with the temperature of 220-300 ℃, the pressure of 0.6-3 MPa and the flow rate of 0.1-1 mL/min, the hydrolysis time is 30-60 min, and the caprolactam yield is more than or equal to 90%.
10. The method for efficient catalytic hydrolysis and reuse of polyamide 6 as claimed in claim 9, wherein the pre-depolymerized material flows from the top to the bottom of the hydrolysis kettle, the water vapor is introduced at the bottom of the hydrolysis kettle, and the water vapor is distributed at the bottom of the hydrolysis kettle>5 pieces/cm 3 。
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