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US-12617748-B2 - Process for recycling of polyethylene terephthalate (pet) waste

US12617748B2US 12617748 B2US12617748 B2US 12617748B2US-12617748-B2

Abstract

The present disclosure relates to a process for production of bis(2-hydroxyethyl) terephthalate (BHET) from polyethylene terephthalate (PET) comprising: (a) effecting partial depolymerization of PET by mixing PET with ethylene glycol in a weight ratio ranging from 1:0.3 to 1:1.5 maintaining temperature of the mixture in a range of 200° C. to 250° C. to obtain a partially depolymerized PET; and (b) effecting depolymerization of the partially depolymerized PET by contacting the partially depolymerized PET with ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:1 to 1:4 in presence of a depolymerization catalyst at a temperature ranging from 170° C. to 200° C. for a time period ranging from 2 hours to 5 hours to produce a crude product mixture comprising bis(2-hydroxyethyl) terephthalate (BHET). The present disclosure also provides a process for recycling of PET from PET waste.

Inventors

  • Kasinath BHAUMIK
  • Anupam ACHARYA
  • Madhu Sudhan BHAGERIA
  • Ashok Chauhan
  • Vyanu VYAS

Assignees

  • FILATEX INDIA LIMITED

Dates

Publication Date
20260505
Application Date
20220121
Priority Date
20210602

Claims (20)

  1. 1 . A process for production of bis(2-hydroxyethyl) terephthalate (BHET) from polyethylene terephthalate (PET), said process comprising the steps of: partially depolymerizing of the polyethylene terephthalate (PET) by mixing the polyethylene terephthalate (PET) with ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:0.3 to 1:1.5 while maintaining temperature of the mixture in a range of 200° C. to 250° C. to obtain a partially depolymerized polyethylene terephthalate (PET), wherein the partial depolymerization is effected in absence of a depolymerization catalyst; and depolymerizing the partially depolymerized polyethylene terephthalate (PET) by contacting the partially depolymerized polyethylene terephthalate (PET) with ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:1 to 1:4 in presence of the depolymerization catalyst at a temperature ranging from 170° C. to 200° C. for a time period ranging from 2 hours to 5 hours, to produce crude product mixture comprising bis(2-hydroxyethyl) terephthalate (BHET).
  2. 2 . The process as claimed in claim 1 , wherein said polyethylene terephthalate (PET) comprises polyethylene terephthalate (PET) waste selected from the group consisting of at least one of: PET bottle flakes, PET yarn, PET thermoformed packages, PET fabric, bright PET yarn waste popcorn, semi dull PET yarn waste popcorn.
  3. 3 . The process as claimed in claim 1 , wherein said polyethylene terephthalate (PET) comprises polyethylene terephthalate (PET) waste having an intrinsic viscosity ranging from 0.5 to 0.8 as measured in 60:40 Phenol:Dichlorobenzene mixed solvent at 25° C., a melting point ranging from 240° C. to 260° C., and an ash content ranging from 0.03% to 2.0% by weight.
  4. 4 . The process as claimed in claim 1 , wherein the step of partial depolymerization of polyethylene terephthalate (PET) comprises: exposing polyethylene terephthalate (PET) to a temperature ranging from 240° C. to 330° C. to obtain molten polyethylene terephthalate (PET); and contacting the molten polyethylene terephthalate (PET) with hot ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:0.3 to 1:1.5 while maintaining the temperature of the mixture in a range of 200° C. to 250° C. to obtain partially depolymerized polyethylene terephthalate (PET).
  5. 5 . The process as claimed in claim 4 , wherein the hot ethylene glycol has a temperature ranging from 180° C. to 190° C.
  6. 6 . A process for recycling of polyethylene terephthalate (PET) from polyethylene terephthalate (PET) waste, said process comprising the steps of: partially depolymerizing the polyethylene terephthalate (PET) waste by mixing the polyethylene terephthalate (PET) waste with ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:0.3 to 1:1.5 while maintaining a temperature of the mixture in a range of 200° C. to 250° C. to obtain a partially depolymerized polyethylene terephthalate (PET); depolymerizing the partially depolymerized polyethylene terephthalate (PET) by contacting the partially depolymerized polyethylene terephthalate (PET) with ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:1 to 1:4 in the presence of a depolymerization catalyst at a temperature ranging from 170° C. to 200° C. for a time period ranging from 2 hours to 5 hours to produce a crude product mixture comprising bis(2-hydroxyethyl) terephthalate (BHET); purifying the crude product mixture to obtain purified bis(2-hydroxy ethyl) terephthalate BHET); and polymerizing the purified bis(2-hydroxyethyl) terephthalate (BHET) in the presence of a polymerization catalyst at a temperature ranging from 200° C. to 300° C. and at a pressure ranging from 50 mbar to 2 mbar for a time period ranging from 2 hours to 5 hours to obtain the recycled polyethylene terephthalate (PET).
  7. 7 . The process as claimed in claim 6 , wherein the polyethylene terephthalate (PET) waste is selected from the group consisting of one or more of: PET bottle flakes, PET yarn, PET thermoformed packages, PET fabric, bright PET yarn waste popcorn, semi dull PET yarn waste popcorn, having an intrinsic viscosity ranging from 0.5 to 0.8 as measured in 60:40 Phenol:Dichlorobenzene mixed solvent at 25° C., a melting point ranging from 240° C. to 260° C., and an ash content ranging from 0.03% to 2.0%.
  8. 8 . The process as claimed in claim 6 , wherein the step of partial depolymerization of the polyethylene terephthalate (PET) waste comprises: exposing the polyethylene terephthalate (PET) waste to a temperature ranging from 240° C. to 330° C. to obtain molten polyethylene terephthalate (PET); and contacting the molten polyethylene terephthalate (PET) with hot ethylene glycol in a weight ratio of PET:ethylene glycol ranging from 1:0.3 to 1:1.5, to obtain partially depolymerized polyethylene terephthalate (PET).
  9. 9 . The process as claimed in claim 6 , wherein the depolymerization catalyst is a metal based catalyst, the metal being selected from the group consisting of at least one of zinc, titanium and antimony, and wherein the polymerization catalyst is selected from the group consisting of Antimony Trioxide, Antimony Triacetate, Antimony Glycolate, and Germanium Dioxide.
  10. 10 . The process as claimed in claim 6 , wherein depolymerizing the partially depolymerized polyethylene terephthalate (PET) step comprises contacting the partially depolymerized polyethylene terephthalate (PET) with the ethylene glycol in the presence of the depolymerization catalyst comprising zinc acetate in an amount ranging from 400 ppm to 1400 ppm.
  11. 11 . The process as claimed in claim 6 , wherein the step of purification of the crude product mixture comprises: filtering the crude product mixture; crystallizing bis(2-hydroxyethyl) terephthalate (BHET) from the filtered crude product mixture; separating crystallized bis(2-hydroxyethyl) terephthalate (BHET) to obtain a cake comprising bis(2-hydroxyethyl) terephthalate (BHET); immersing the cake in a hot water in a weight ratio ranging from 1:4 to 1:8 to obtain an immersion mixture, said hot water having temperature ranging from 90° C. to 98° C.; recrystallizing the bis(2-hydroxyethyl) terephthalate (BHET) from the immersion mixture; and separating the recrystallized bis(2-hydroxyethyl) terephthalate (BHET) to obtain purified bis(2-hydroxyethyl) terephthalate (BHET).
  12. 12 . A method for production of bis(2-hydroxyethyl) terephthalate (BHET) from polyethylene terephthalate (PET), comprising: feeding polyethylene terephthalate (PET) and ethylene glycol into a first reaction vessel, wherein polyethylene terephthalate (PET) and the ethylene glycol are in a weight ratio of PET:ethylene glycol ranging from 1:0.3 to 1:1.5; maintaining the first reaction vessel at a temperature in a range of 200° C. to 250°, resulting in partially depolymerized polyethylene terephthalate (PET); feeding the partially depolymerized polyethylene terephthalate (PET) and ethylene glycol into a second reaction vessel having a depolymerization catalyst, wherein the partially depolymerized polyethylene terephthalate (PET) and the ethylene glycol are in a weight ratio of PET:ethylene glycol ranging from 1:1 to 1:4; and maintaining the second reaction vessel at a temperature ranging from 170° C. to 200° C. for a time period ranging from 2 hours to 5 hours, resulting in a crude product mixture comprising bis(2-hydroxyethyl) terephthalate (BHET), wherein the first reaction vessel may be the same or different from the second reaction vessel; and wherein the depolymerization catalyst is not present in the first reaction vessel when the polyethylene terephthalate (PET) and ethylene glycol are fed into the first reaction vessel.
  13. 13 . The system method as claimed in claim 12 , wherein said polyethylene terephthalate (PET) comprises polyethylene terephthalate (PET) waste selected from the group consisting of at least one of: PET bottle flakes, PET yarn, PET thermoformed packages, PET fabric, bright PET yarn waste popcorn, semi dull PET yarn waste popcorn.
  14. 14 . The method as claimed in claim 12 , wherein said polyethylene terephthalate (PET) comprises polyethylene terephthalate (PET) waste having an intrinsic viscosity ranging from 0.5 to 0.8 as measured in 60:40 Phenol:Dichlorobenzene mixed solvent at 25° C., a melting point ranging from 240° C. to 260° C., and an ash content ranging from 0.03% to 2.0% by weight.
  15. 15 . The method as claimed in claim 12 , further comprising heating the polyethylene terephthalate (PET) in the first vessel to a temperature ranging from 240° C. to 330° C. to obtain molten polyethylene terephthalate (PET), and receiving hot ethylene glycol in the first vessel and mixing the received hot ethylene glycol with the molten polyethylene terephthalate (PET) in a weight ratio of PET:ethylene glycol ranging from 1:0.3 to 1:1.5, while maintaining the mixture at a temperature in a range of 200° C. to 250° C., to obtain the partially depolymerized polyethylene terephthalate (PET).
  16. 16 . The method as claimed in claim 15 , wherein the hot ethylene glycol is received into the first vessel at a temperature ranging from 180° C. to 190° C.
  17. 17 . The method as claimed in claim 12 , wherein the depolymerization catalyst comprises zinc acetate present in the second vessel in an amount ranging from 400 ppm to 1400 ppm.
  18. 18 . The process as claimed in claim 1 , further comprising: purifying the crude product mixture to obtain purified bis(2-hydroxy ethyl) terephthalate (BHET); and polymerizing the purified bis(2-hydroxyethyl) terephthalate (BHET) in the presence of a polymerization catalyst at a temperature ranging from 200° C. to 300° C. and at a pressure ranging from 50 mbar to 2 mbar for a time period ranging from 2 hours to 5 hours to obtain the recycled polyethylene terephthalate (PET).
  19. 19 . The process as claimed in claim 18 , wherein the step of purifying comprises: filtering the crude product mixture; crystallizing bis(2-hydroxyethyl) terephthalate (BHET) from the filtered crude product mixture; separating crystallized bis(2-hydroxyethyl) terephthalate (BHET) to obtain a cake comprising bis(2-hydroxyethyl) terephthalate (BHET); immersing the cake in a hot water in a weight ratio ranging from 1:4 to 1:8 to obtain an immersion mixture, said hot water having temperature ranging from 90° C. to 98° C.; recrystallizing the bis(2-hydroxyethyl) terephthalate (BHET) from the immersion mixture; and separating the recrystallized bis(2-hydroxyethyl) terephthalate (BHET) to obtain purified bis(2-hydroxyethyl) terephthalate (BHET).
  20. 20 . The process as claimed in claim 6 , wherein the depolymerizing is conducted at a temperature ranging from 180° C. to 190° C.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a national stage application under 35 U.S.C. § 371 of PCT/IB2022/050519, filed Jan. 21, 2022, which claims priority from Indian Patent Application No. IN202121024616, filed Jun. 2, 2021, the entirety of which are expressly incorporated herein by reference. TECHNICAL FIELD The present disclosure generally relates to the field of recycling of plastic waste including, but not limited to flakes, polymers and post-consumer recycled plastic. More specifically, the present disclosure relates to a process for 5 recycling of polyethylene terephthalate (PET) waste. Another aspect of the present disclosure relates to a process for production of bis(2-hydroxyethyl) terephthalate (BHET) from polyethylene terephthalate (PET). BACKGROUND Background description includes information that may be useful in understanding the present invention, and each reference cited herein is expressly incorporated herein by reference in its entirety. It is not an admission that any of the information provided herein is prior-art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art. Millions of tons of plastic waste are produced every year in 15 manufacturing of various products. A significant proportion of the plastic waste is accounted for by polyester waste such as PET bottles, thermoformed packages, polyester fiber, yarn and fabric waste and the likes. Rigorous research has been done, at least in the last 2 decades, in the area of polyester recycling to effectively make use of such recycled polyester in various applications. One of the method that finds limited industrial utility in recycling of plastic waste, particularly, polyester waste is conversion thereof into monomers by deglycol reaction (also known as deglycolization reaction) i.e., reacting the polymer at a temperature of about 250° C. or more and at a pressure of 1 mmHg or less in presence of deglycol catalyst such as a metal compound catalyst to form 25 the monomers and then converting them into polymers to produce different kind of yams. Hu et al. in “Synthesis of poly(ethylene terephthalate) based on glycolysis of waste PET fiber”, Journal of Macromolecular Science, Part A; Pure and Applied; Chemistry; Volume 57, 2020—Issue 6 (doi.org/10.1080/10601325.2019.1709498) discloses glycolysis as a chemical recycling route for waste poly(ethylene terephthalate) (PET), wherein glycolysis of waste PET fiber was carried out under nitrogen atmospheric condition with excess ethylene glycol (EG) as glycolysis agent and zinc acetate (Zn(Ac)2) as catalyst, contents whereof is incorporated herein in its entirety by way of reference. US20040182782A1 discloses a method of obtaining BHET of high purity efficiently from an EG (ethylene glycol) solution containing crude BHET (bis(2-hydroxyethyl) terephthalate), especially a decomposition product solution obtained by decomposing a polyester containing PET (polyethylene terephthalate) as a main component, by use of EG, while minimizing by-production of impurity components such as DEG (diethylene glycol). DEG ester and oligomers, contents whereof is incorporated herein in its entirety by way of reference. CN107266664A discloses a kind of reclaim of PET scrap technique, which is related to resource regeneration field, solves the recovery problem of colored polyester waste material, comprise the following steps: S1, pet waste crashed, cleans, dry. It is complete that S2, pet waste and EG, catalyst add depolymerization reaction under reactor, 170˜210 DEG C. of constant temperature; S3, 125˜145 DEG C. are cooled to, heat filtering obtains first-time filtrate and unreacted PET; S4, first-time filtrate distillation obtain EG; Liquid after S5, distillation adds solvent, and heat filtering obtains secondary filtrate and BHET oligomer; Added in S6, secondary filtrate and three filtrates are obtained after decolorising agent, heat filtering; S7, three filtrate crystallisation by cooling separate out acicular crystal, are filtrated to get monomer BHET, and in 60 DEG C. of dryings; Final minification gathers under precondensation under the conditions of S8, low vacuum, high vacuum condition; S9, Cast Strip, cooling, pelletizing and drying, finally obtain PET grain products, contents whereof is incorporated herein in its entirety by way of reference. EP0723951A1 discloses a process to prepare very high purity bis(2-hydroxyethyl) terephthalate, using waste polyethylene terephthalate (PET) as the starting product. More specifically, the process is used to prepare BHET through the reaction of waste PET with excess ethylene glycol (EG), and preferably at a temperature of 190-210° C., in the presence of a transesterification catalyzer. This is followed by a series of separations and crystallisations (for which three different methods are proposed) to obtain a pure, chemically defined product that does not contain any of the impurities tha