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EP-4735413-A1 - CRYSTALLIZATION METHOD FOR PURIFIED TEREPHTHALIC ACID

EP4735413A1EP 4735413 A1EP4735413 A1EP 4735413A1EP-4735413-A1

Abstract

The invention relates to a method for preparing crystalline purified terephthalic acid (PTA) with an average crystal size of approx. 50-150 microns, comprising, in the following order, the steps of: a) providing an aqueous PTA solution of purified metalated salt of terephthalic acid (pH 7); b) heating the solution to a maximum crystallization temperature; c) adjusting the solution to a pH of 5; d) subjecting the solution to a cooling-heating cycle to obtain growing PTA crystals, wherein the solution is cooled to a minimum crystallization temperature and subsequently heated to the maximum crystallization temperature; e) at the maximum crystallization temperature adjusting the pH of the PTA solution to 1 – 3 for full precipitation of crystalline PTA, and f) filtering the PTA solution to collect crystalline PTA; g) washing the filtered crystals with cold water; h) drying the crystals.

Inventors

  • ANDERSON, Samantha
  • URAN, Pelin
  • BILA, Hale

Assignees

  • DePoly SA

Dates

Publication Date
20260506
Application Date
20240607

Claims (15)

  1. 1. A crystallization method for purified terephthalic acid (PTA) to obtain crystalline PTA with an average crystal size of approx. 50-150 microns, the method comprising in the following order the steps of: a. providing in a reactor a PTA solution of 7-13 wt% of purified metalated salt of terephthalic acid (M-PTA) in water at a pH of 7; b. heating the PTA solution to a maximum crystallization temperature; c. adjusting the PTA solution to a pH of 5 using an acid; d. subjecting the PTA solution to a cooling-heating-cycle for at least 1 time, preferably at least 3 times, more preferably 5 to 8 times, to obtain growing PTA crystals, wherein the solution is cooled to a minimum crystallization temperature and subsequently heated to the maximum crystallization temperature; e. at the maximum crystallization temperature adjusting the pH of the PTA solution to 1 - 3 using an acid for full precipitation of crystalline PTA; f. at the maximum crystallization temperature filtering the PTA solution to collect crystalline PTA; g. washing the filtered crystalline PTA with cold water; h. drying the washed crystalline PTA.
  2. 2. Method according to claim 1, wherein the minimum crystallization temperature and the maximum crystallization temperature of the cooling-heating-cycle are chosen and set between 40-85 °C, preferably selected from the range of 40-45 °C, 45-50 °C, 50-55 °C, 55-60 °C, 60-65 °C, 65-70 °C, 70-75 °C, and 75-80 °C.
  3. 3. Method according to claim 2, wherein an actual minimum crystallization temperature of the PTA solution in the reactor is up to approx. 3°C lower than the set minimum crystallization temperature and/or an actual maximum crystallization temperature of the PTA solution in the reactor is up to approx. 3°C higher than the set maximum crystallization temperature.
  4. 4. Method according to one of the preceding claims, wherein the difference between the minimum crystallization temperature and the maximum crystallization temperature is in a range of 5-40°C, preferably 5-20°C, more preferably 5-10°C.
  5. 5. Method according to one of the preceding claims, wherein the method is performed under normal atmospheric pressure.
  6. 6. Method according to one of the preceding claims, wherein the cooling and/or heating is performed at a rate of approx. 5°C per 10-20 minutes.
  7. 7. Method according to one of the preceding claims, wherein one cooling-heating-cycle lasts approx. 10 to 40 minutes.
  8. 8. Method according to one of the preceding claims, wherein a cooling period and/or a heating period last approx. 5 to 20 minutes.
  9. 9. Method according to one of the preceding claims, wherein in each cooling-heating- cycle the maximum crystallization temperature is kept for approx. 1 to 3 minutes before the next cooling-heating-cycle or the next step starts.
  10. 10. Method according to one of the preceding claims, wherein in each cooling-heating- cycle the heating starts immediately when the minimum crystallization temperature is reached.
  11. 11. Method according to one of the preceding claims, wherein the metalated salt of terephthalic acid (M-PTA) is either sodium terephthalic acid (Na-PTA) or potassium terephthalic acid (K-PTA).
  12. 12. Method according to one of the preceding claims, wherein the M-PTA is obtained from depolymerization of waste PET via alkaline hydrolysis.
  13. 13. Method according to one of the preceding claims, wherein the M-PTA is purified using graphite, activated carbon and molecular sieve to remove organic and inorganic contaminants.
  14. 14. Method according to one of the preceding claims, wherein the acid of step c) and/or step e) is selected from the group of acetic acid, HCI, H2SO4, formic acid, propionic acid and butyric acid.
  15. 15. Method according to one of the preceding claims, wherein the cold water of step g) has a temperature of approx. 10 to 20°C.

Description

Crystallization method for purified terephthalic acid Technical Field The invention relates to crystallization method for purified terephthalic acid (PTA) to obtain crystalline PTA with an average crystal size of approx. 50-150 microns. Technical Background Poly(ethylene terephthalate), widely known as PET, is a semicrystalline thermoplastic polyester that is used in a variety of industries in the form of fibres, sheets, films, and bottles. Its stability, high mechanical strength, high resistance to atmospheric and biological agents, and good aesthetic appearance has led to its prevalence in both the commercial and industrial sectors. While PET has become an inextricable part of our lives, environmental concerns have been raised about its pollution in our ocean and landfills. The environmental effects of PET production are not only limited to postconsumer PET contaminating the landfills It has also been reported that while other industrial sectors can lower their carbon footprint, the petrochemical industry which produces PET will ultimately increase their greenhouse gas emissions with increased PET production, thereby eroding climate benefits. The most common industrial synthesis route of PET is through the polycondensation of ethylene glycol (EG) and dimethyl terephthalate (DMT) or purified terephthalic acid (PTA) using a continuous melt-phase polymerization process with temperatures of approximately 280°C. The base chemicals for this process (EG, DMT, and PTA) are typical bulk chemicals that the petrochemical industry obtains from catalytic reforming of petroleum naptha to paraxylene. Therefore, closing the recycling loop has a cascading effect from removing post-consumer waste from our environment to lowering greenhouse gas emission by increasing the supply of PTA within the market, and decreasing our reliance of PTA from the petroleum industry. Following the consumption of PET, either commercially or industrially, users typically recycle the product(s) via four distinct methods, which are referred to as primary through quaternary recycling depending on the quality of the recycled product While primary recycling exclusively deal with industrial PET scrap and salvage, secondary recycling physically reprocesses consumer PET through grinding, washing, drying and reprocessing. However, the quality of PET obtained through secondary recycling is not virgin, and therefore much of it ends up being incinerated to recovery the energy content (quaternary recycling). Ultimately, tertiary recycling, or the depolymerization of PET to its starting monomers is the ideal method to close the recycling loop, as the monomers can be resold back to the chemical industry to form virgin PET, or other products. An effective, inexpensive, robust and practical technology for degrading plastic waste, such as PET material, and simultaneously producing terephthalic acid (TPA), and/or ethylene glycol (EG) and/or other monomers that form plastic material is described in W02020173961 by the same applicant. W02020173961 (incorporated herein by reference in its entirety) provides a method of alkaline hydrolysis of one or more plastic polymers into terephthalic acid (TPA) and/or ethylene glycol (EG) and/or other monomers that form the one or more plastic polymers. The method may output terephthalic acid that is contaminated or otherwise of a quality that requires further purification before further processing and use. Current methods of purifying TPA are energy intensive, and economically inefficient. U.S. provisional application No. 63425771 by the same applicant (incorporated herein by reference in its entirety) describes a method of purifying terephthalic acid. The method includes contacting unpurified terephthalic acid with graphite, activated carbon, and molecular sieve to provide a reaction mixture, stirring the reaction mixture for a first certain period of time, filtering the reaction mixture, to provide a reaction mixture filtrate, providing graphite, activated carbon, and molecular sieve to the reaction mixture filtrate, stirring the reaction mixture filtrate for a second certain period of time, filtering the reaction mixture filtrate, to provide a reaction output solution and precipitating purified terephthalic acid (PTA) from the reaction output solution. For PTA to be processed into polyethylene terephthalate (PET) and other polyester based polymers with the TPA monomer, crystalline PTA with a crystal size of 50 to 150 microns is required. This is to allow efficient handling and flowability, and also to allow the optimal ratio of the PTA and other monomer (ethylene glycol in the case of PET) to form a paste suitable for the polymerisation process. Common methods of purifying TPA to obtain purified terephthalic acid (PTA) typically include recrystallization steps, which require high temperatures (>100 °C) and pressures (>1 atm) to get the crystal of PTA to the right size (avg. 100 microns) for a later polycondensation proces