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CN-122029223-A - Plastic processing using subcritical/supercritical fluid

CN122029223ACN 122029223 ACN122029223 ACN 122029223ACN-122029223-A

Abstract

A process for recycling difficult-to-recycle plastics such as polyvinyl chloride (PVC) and/or mixed plastic streams is provided. The plastic may be an industrial water plastic or a mixed municipal waste plastic in which PVC is present. In the present disclosure, a sub-critical or supercritical fluid depolymerization process using an alcohol (e.g., methanol) is employed to convert PVC to a controlled mixture of organic products, such as C 2 -C 4 compounds.

Inventors

  • ORLOV ALEXANDER
  • R. Grubbs
  • T. Gu He
  • S. Batia
  • M. Guhe

Assignees

  • 纽约州州立大学研究基金会

Dates

Publication Date
20260512
Application Date
20241018
Priority Date
20231020

Claims (20)

  1. 1. A process for recycling plastic, the process comprising: the waste plastic stream comprising at least PVC is depolymerized in a reactor at a temperature below the decomposition temperature of polyvinyl chloride (PVC) and in the presence of a subcritical or supercritical fluid comprising an alcohol.
  2. 2. The process of claim 1, wherein the alcohol has from 1 to 8 carbon atoms.
  3. 3. The process of claim 2, wherein the alcohol is ethanol.
  4. 4. The process of claim 1, wherein the depolymerization is performed in the presence of a reactive clay, aluminosilicate, a base formed by neutralizing hydrochloric acid, or any combination thereof.
  5. 5. The process of claim 1, wherein the subcritical or supercritical fluid further comprises water.
  6. 6. The process of claim 5, wherein the subcritical or supercritical fluid comprises ethanol and water.
  7. 7. The process of claim 5, wherein the subcritical or supercritical fluid has a water to alcohol ratio of about 1:1 to about 10:1.
  8. 8. The process of claim 5, wherein the depolymerization is performed in the presence of a reactive clay, aluminosilicate, a base formed by neutralizing hydrochloric acid, or any combination thereof.
  9. 9. The process of claim 1, wherein the depolymerization is carried out at a pressure of about 0.1 atmospheres to about 100 atmospheres.
  10. 10. The process of claim 1, wherein the decomposition temperature is about 500 ℃ or greater and the depolymerization temperature is about 200 ℃ to less than 500 ℃.
  11. 11. The process of claim 1, wherein the depolymerization produces a halogen-free product having 2 to 12 carbon atoms.
  12. 12. The process of claim 1, wherein the depolymerization produces a halogen-free product having 2 to 4 carbon atoms.
  13. 13. The process of claim 11, wherein the halogen-free product comprises at least poly (vinyl ether).
  14. 14. The process of claim 1, further comprising monitoring polymer cluster formation for depolymerization.
  15. 15. The process of claim 14, wherein the monitoring comprises at least one of synchronous wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), inelastic X-ray scattering (IXS), and Molecular Dynamics (MD) simulation.
  16. 16. The process of claim 15, wherein the monitoring further comprises Infrared (IR) spectroscopy.
  17. 17. The process of claim 1, further comprising separating and recovering a reaction product formed from depolymerization.
  18. 18. The process of claim 17, wherein the separating comprises isothermal pressure drop after depolymerization or adding a clay-based emulsion to a product formed by depolymerization.
  19. 19. The process of claim 17, wherein the recovering comprises a fractionation process.
  20. 20. A recycling apparatus comprising: a reactor configured to perform a depolymerization reaction at a temperature below the decomposition temperature of a recyclable plastic stream comprising at least PVC, wherein the depolymerization reaction is performed in the presence of a subcritical or supercritical fluid comprising an alcohol.

Description

Plastic processing using subcritical/supercritical fluid Cross Reference to Related Applications The present application claims priority from U.S. provisional application Ser. No. 63/591,955 filed on 10/20 of 2023, the entire contents of which are incorporated herein by reference. Background The present disclosure relates to recycling of plastics, and more particularly, to a process for recycling difficult-to-recycle plastics such as polyvinyl chloride (PVC) and/or mixed plastic streams. Approximately 3200 ten thousand tons of mixed plastic waste are sent to U.S. landfills each year. There are several reasons for this, but mainly due to the lack of a robust market, the inability of recycled plastics to meet the proper specifications for product packaging or preservation, and consumer knowledge and action. Supercritical fluids (SCF) have been used to recycle plastics that are difficult to recycle, such as PVC or PVC mixed with other plastics. Notably, SCF has been investigated for a range of applications related to polymer degradation and depolymerization. Depending on the polymer, solvent and processing conditions, a range of depolymerization or degradation mechanisms are possible. Polymers having backbone linkages susceptible to solvolysis, such as polyesters, polyamides, and polycarbonates, are particularly suitable for depolymerization in SCF to well-defined products. Depolymerization of polyesters with supercritical water (scH 2 O), supercritical methanol (scMeOH) and supercritical ethanol (scEtOH) has been reported. One example is a pilot scale process for depolymerizing polyethylene terephthalate (PET) in bottles with scMeOH. Large-scale treatment of PET with scEtOH has not been reported, but large-scale depolymerization of lignin with scEtOH has been studied. SCF has also been found to be effective in debrominating flame retardant additives in plastics. For polyolefins and related polymers having an all-carbon backbone, treatment with SCF generally results in a mixture of products, especially with highly oxidative scH 2 O. For example, polyethylene (PE) has been degraded by scH 2 O treatment to olefins and mixtures of olefins. Polyvinyl alcohol (PVA) exposed to scH 2 O in the presence of sodium hydroxide has been reported to form a mixture of C 2-C18 carboxylic acids. Treatment of Polystyrene (PS) with scMeOH at temperatures (340-420 ℃) and pressures (10-30 MPa) well above the critical point (tc=240 ℃, pc=8.1 MPa) was found to produce mixtures of styrene, ethylbenzene, toluene and other derivatives. It has also been found that degradation of epoxy, phenolic and Polyetheretherketone (PEEK) resins with scH 2 O and scMeOH produces a mixture of products. The case of PVC is more complex. Although a substantial portion of the PVC-containing material can be collected for mechanical recycling, the presence of PVC in the mixed plastic waste stream can lead to processing difficulties. Direct pyrolysis of PVC results in the formation of a chlorinated oil mixture that requires dechlorination prior to further use. PVC typically breaks down upon heating before depolymerization is observed, so strategies involving PVC catalyzed dichlorination are more common. Supercritical H 2 O treatment has been studied to convert a range of plastics into oil mixtures intended for conversion into fuels. Currently, the use of SCF to treat PVC waste has focused on degradation to gas/oil mixtures. However, these attempts have not focused on optimizing the selectivity of the process to produce discrete products from complex mixtures to enable plastics to be converted to chemical raw materials. Increasing the reaction selectivity by adding catalysts and/or sacrificial reagents has only been applicable to superheated steam conditions, however, no attempt has been made to convert this process to SCF conditions. Disclosure of Invention The present disclosure provides a process for recycling difficult-to-recycle plastics such as PVC and/or mixed plastic streams. The plastic may be an industrial water plastic or a mixed municipal waste plastic in which PVC is present. In embodiments of the present disclosure, a depolymerization process using subcritical or supercritical fluid of an alcohol is employed to convert PVC to a controlled mixture of organic products, such as C 2-C4 compounds. The process of the present disclosure can be used for the selective depolymerization of plastic materials, such as PVC, which are difficult to depolymerize thermally in both pure waste streams and model mixed waste streams with other plastics. In some embodiments, depolymerization of PVC into useful products is accomplished using a mixture of scEtOH or scEtOH and scH 2 O. A combination of simultaneous X-ray techniques (WAXS, SAXS, XPCS and IXS) can be used in combination to detect in situ structure and kinetics of clusters and polymer chains during the depolymerization process. These experimental results can be used to validate models of Molecular Dynamics (