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CN-122011502-A - Waste plastic recycling method

CN122011502ACN 122011502 ACN122011502 ACN 122011502ACN-122011502-A

Abstract

The invention belongs to the technical field of plastic recovery, and particularly relates to a waste plastic recovery processing method which comprises the following steps of S1, preprocessing, S2, carrying out low-temperature critical extraction, namely, sending the preprocessed plastic into a high-pressure reaction kettle, injecting an extraction solvent into the high-pressure reaction kettle, extracting at a temperature lower than the melting point of the plastic by 50-100 ℃ and under a condition higher than the critical pressure of the extraction solvent, separating and removing additives and micromolecular impurities, S3, carrying out in-situ reconstruction, namely, adding a reconstruction agent into the high-pressure reaction kettle after extraction, carrying out molecular chain repair reaction under a supercritical fluid atmosphere, and S4, extruding and granulating a reconstructed plastic melt. The invention is extracted at the temperature 50-100 ℃ lower than the melting point of the plastic, the plastic polymer main body keeps solid state and does not melt, the thermal oxygen chain scission reaction is avoided, the molecular chain structure is reserved, and the recombination realizes the reconnection and the growth of the molecular chain.

Inventors

  • XIE ZHAOHUA

Assignees

  • 重庆诺腾包装制品有限公司

Dates

Publication Date
20260512
Application Date
20260317

Claims (10)

  1. 1. The waste plastic recycling method is characterized by comprising the following steps of: s1, preprocessing, namely sorting, crushing and cleaning waste plastics; S2, low-temperature critical extraction, namely feeding the pretreated plastic into a high-pressure reaction kettle, injecting an extraction solvent into the high-pressure reaction kettle, extracting at a temperature 50-100 ℃ lower than the melting point of the plastic and under a pressure higher than the critical pressure of the extraction solvent, and separating and removing additives and micromolecular impurities; s3, in-situ reconstruction, namely adding a reconstruction agent into the high-pressure reaction kettle after extraction, and carrying out molecular chain repair reaction in a supercritical fluid atmosphere; And S4, extruding and granulating the reconstructed plastic melt.
  2. 2. The method for recycling waste plastics according to claim 1, wherein in the step S2, the extraction solvent comprises a main solvent and a cosolvent, wherein the main solvent is carbon dioxide, propane or dimethyl ether, the cosolvent is ethanol, acetone or ethyl acetate, the main solvent is pressurized and liquefied, the main solvent and the cosolvent are introduced into a mixer, and the mixture is introduced into a high-pressure reaction kettle, wherein the volume ratio of the main solvent is 60-90%.
  3. 3. The method for recycling waste plastics according to claim 1, wherein in the step S2, the extraction pressure is 8-25MPa, the extraction time is 30-120min, the rate of introducing the extraction solvent into the high-pressure reaction kettle is 0.5-5L/min, and the weight ratio of the extraction solvent to the plastics is (3-10): 1.
  4. 4. The method for recycling waste plastics according to claim 1, wherein in step S2, the extraction solvent discharged from the high-pressure reactor is introduced into a rectifying tower, and the additive and the small molecular impurities in the extraction phase are separated by the rectifying tower, thereby obtaining the reusable extraction solvent.
  5. 5. The method for recycling waste plastics according to claim 1, wherein in the step S3, the reconfiguration agent is a four-arm star-shaped copolymer having triazine-1, 3, 5-triton amide supramolecular core, polycaprolactone flexible connecting arm and glycidyl methacrylate-butyl methacrylate copolymer side chain, and the structural general formula is: , Wherein S-T is triazine-1, 3, 5-trityl formamide supermolecule unit, PCL is polycaprolactone, molecular weight is 2000-5000, GMA-co-BMA is random copolymer side chain of glycidyl methacrylate and butyl methacrylate, polymerization degree m=10-30, and molar ratio of GMA to BMA is 3:1 to 1:1.
  6. 6. The method for recycling waste plastics according to claim 5, wherein the weight average molecular weight of the reconstruction agent is 3.0X10 4 -6.0×10 4 , the molecular weight distribution is less than or equal to 1.5, and the epoxy equivalent is 350-450g/eq.
  7. 7. The method for recycling waste plastics according to claim 5, wherein the preparation method of the reconstruction agent comprises the steps of: Synthesizing triazine-1, 3, 5-trityl amide supermolecular core S-T; S-T and double-end hydroxyl polycaprolactone are subjected to esterification reaction to synthesize an S-T-PCL-S-T prepolymer; Reacting S-T-PCL-S-T with 2-bromoisobutyryl bromide, and introducing an ATRP initiation site to obtain a macromolecular initiator; The method comprises the steps of taking a macromolecular initiator as a raw material, and grafting a copolymer side chain of glycidyl methacrylate and butyl methacrylate through atom transfer radical polymerization to obtain the reconstruction agent.
  8. 8. The method for recycling waste plastics according to claim 5, wherein the step S3 is performed in a carbon dioxide atmosphere, and specifically comprises: s31, adding a reconstruction agent into the high-pressure reaction kettle, wherein the addition amount of the reconstruction agent is 1.0-5.0% of the mass of the plastic; s32, mixing for 5-10min at 150-180 ℃ to uniformly disperse the reconstruction agent; s33, cooling to 80-100 ℃, preserving heat for 10-20min, and promoting supermolecule self-assembly; S34, heating to 200-240 ℃ and reacting for 15-30min to realize covalent chain extension.
  9. 9. The method for recycling waste plastics according to claim 5, wherein in the step S1, during cleaning, the crushed plastics are immersed in a cleaning solution containing a cationic surfactant, and the cleaning solution is cleaned for 20-40min at 60-75 ℃, and the residual amount of the cationic surfactant on the surface of the cleaned plastics is controlled to be 0.01-0.1wt%, wherein the cationic surfactant is cetyl trimethyl ammonium bromide or a quaternary ammonium salt surfactant with a C12-C18 alkyl chain; In the step S2, the process is carried out under the supercritical carbon dioxide atmosphere, the residual cationic surfactant on the surface of the plastic forms reverse micelle, and the extracted additive is wrapped to prevent the additive from redeposition on the surface of the plastic; In the step S3, the quaternary ammonium cation of the cationic surfactant remained on the surface of the plastic and the triazine ring of the S-T unit form cation-pi interaction, and meanwhile, the C16 long chain of the cationic surfactant and the PCL chain segment are entangled to jointly promote the oriented self-assembly of the reconstruction agent.
  10. 10. The method for recycling waste plastics according to claim 9, wherein the cleaning solution comprises, by mass, 0.5-2.0 parts of cetyl trimethyl ammonium bromide, 0.3-1.5 parts of a nonionic surfactant, 1.0-3.0 parts of a bio-based solvent, 0.1-0.3 parts of a complexing agent and 93.2-98.1 parts of water.

Description

Waste plastic recycling method Technical Field The invention belongs to the technical field of plastic recovery, and particularly relates to a waste plastic recovery treatment method. Background With the continuous increase of the consumption of plastic products, the treatment and recycling of waste plastics has become a global environmental challenge. At present, waste plastic recovery mainly faces two technical bottlenecks: First, the problem of performance degradation due to thermal oxidative aging. Conventional mechanical recovery processes typically employ high temperature melt reconstitution (temperature >200 ℃) in which polymer molecular chains undergo chain scission reactions in the presence of high temperature shear and oxygen, with a significant decrease in molecular weight. Taking polyethylene terephthalate (PET) as an example, the intrinsic viscosity after recovery is generally reduced from 0.75-0.85dL/g of virgin materials to below 0.55-0.65dL/g, and the mechanical properties of the materials can be reduced every time the recycling is carried out, so that the materials can only be degraded for low added value products. Second, complex additive mixing causes performance runaway problems. The waste plastic raw product usually contains a plurality of additives such as plasticizer, flame retardant (such as polybrominated diphenyl ether and hexabromocyclododecane), color master, light stabilizer, heat stabilizer and the like. In the traditional recovery process, the additives cannot be effectively separated, react with each other and decompose and carbonize in a high-temperature melting state, so that not only is the regenerated material produced pungent smell and micromolecular substances separated out to pollute, but also the performance of the regenerated material is greatly fluctuated and uncontrollable. In particular to waste household electrical appliance plastics containing brominated flame retardants, which are often decomposed to generate toxic corrosive gas after recovery, thereby severely restricting the high-value utilization of the waste household electrical appliance plastics. Existing chemical recovery techniques (e.g., alcoholysis, hydrolysis, pyrolysis) can depolymerize polymers to monomers or oligomers, but require very high feed purity. The complex additives in the waste plastics can poison the catalyst and pollute depolymerized products, and the process flow is long, the energy consumption is high and the economy is poor. Pyrolysis technology can process low residue mixed waste plastics, but the product is a mixed oil product rather than a high value polymeric material. Disclosure of Invention The invention aims to provide a waste plastic recycling method for solving the problems. In order to solve the problems, the technical scheme adopted by the invention is that the waste plastic recycling method comprises the following steps: s1, preprocessing, namely sorting, crushing and cleaning waste plastics; S2, low-temperature critical extraction, namely feeding the pretreated plastic into a high-pressure reaction kettle, injecting an extraction solvent into the high-pressure reaction kettle, extracting at a temperature 50-100 ℃ lower than the melting point of the plastic and under a pressure higher than the critical pressure of the extraction solvent, and separating and removing additives and micromolecular impurities; s3, in-situ reconstruction, namely adding a reconstruction agent into the high-pressure reaction kettle after extraction, and carrying out molecular chain repair reaction in a supercritical fluid atmosphere; And S4, extruding and granulating the reconstructed plastic melt. In step S2, the extraction solvent comprises a main solvent and a cosolvent, wherein the main solvent is carbon dioxide, propane or dimethyl ether, the cosolvent is ethanol, acetone or ethyl acetate, the main solvent is pressurized and liquefied, the main solvent and the cosolvent are introduced into a mixer, and after being mixed, the main solvent and the cosolvent are introduced into a high-pressure reaction kettle, and the volume ratio of the main solvent in the mixer is 60-90%. Further, in the step S2, the extraction pressure is 8-25MPa, the extraction time is 30-120min, the rate of introducing the extraction solvent into the high-pressure reaction kettle is 0.5-5L/min, and the weight ratio of the extraction solvent to the plastic is (3-10): 1. In step S2, the extraction solvent discharged from the autoclave is introduced into a rectifying column, and the additive and the small molecular impurities in the extraction phase are separated by the rectifying column, thereby obtaining the reusable extraction solvent. Further, in step S3, the reconstitution agent is a four-arm star-shaped copolymer having a triazine-1, 3, 5-triton amide supramolecular core, a polycaprolactone flexible connecting arm and a glycidyl methacrylate-butyl methacrylate copolymer side chain, and the structural general formula is