The acetate anion promotes hydrolysis of poly(ethylene terephthalate) in ionic liquid-water mixtures
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
A circular plastic economy reduces raw material consumption and discourages pollution. Chemical recycling upgrades the quality of recyclate and is a complementary approach to thermomechanical recycling of plastic waste. This study investigated the use of aprotic and protic ionic liquids (ILs) as solvents for chemical recycling by the hydrolysis of the most common polyester plastic, poly(ethylene terephthalate) (PET). Combinations of three types of cations (aprotic 1-alkyl-3-methylimidazolium, protic 1-methylimidazolium and protic 1,5-biazocyclo-[4.3.0]non-5-enium) combined with a range of anions (acetate, chloride, methanesulfonate, hydrogen sulfate, methyl sulfate, trifluoromethanesulfonate and chlorozincate) were used to hydrolyse PET in the presence of 15 wt% water as the co-solvent and reagent. PET conversion under the screening conditions (180 °C, 3 h, 5% PET loading) varied between 1 and 100%, with ILs containing the acetate anion enabling >97% PET conversion irrespective of the cation. Acidification with aqueous HCl recovered crude crystallised terephthalic acid (TPA). Significant crude yields (46–93%) were only observed for the acetate ILs. The purity of the crude TPA was 34–98%, with 1-ethy-3-methylimidazolium acetate, [C2C1im][OAc], and 1-methylimidazolium acetate, [C1Him][OAc], yielding more and purer TPA than 1,5-biazocyclo-[4.3.0]non-5-enium acetate, [DBNH][OAc]. TPA solubility, PET conversion and TPA yield generally correlated well with increasing pKa and higher hydrogen bond acceptor strength of the IL anion, suggesting that the depolymerisation mechanism in the acetate IL water mixtures is base catalysed. The screening identifies aqueous mixtures of the (pseudo)-protic IL [C1Him][OAc] as promising catalytic solvent component for the chemical recycling of PET at an industrially feasible temperature, due to high isolated TPA yields and purity achieved at a low solvent cost ($1.74–2.15 per kg). However, an effective separation approach for the monomers TPA and ethylene glycol from the solvent remains to be developed.
Date Issued
2025-09-22
Date Acceptance
2025-08-07
Citation
Green Chemistry, 2025, 27 (37), pp.11475-11490
ISSN
1463-9262
Publisher
Royal Society of Chemistry
Start Page
11475
End Page
11490
Journal / Book Title
Green Chemistry
Volume
27
Issue
37
Copyright Statement
This journal is © The Royal Society of Chemistry 2025. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
License URL
Identifier
10.1039/d5gc02409a
Subjects
BIOMASS
CATALYSTS
CELLULOSE
Chemistry
Chemistry, Multidisciplinary
ESTERIFICATION
GLYCOLYSIS
Green & Sustainable Science & Technology
PET DEGRADATION
Physical Sciences
Science & Technology
Science & Technology - Other Topics
SOLVENT
TEREPHTHALIC ACID
WASTE
Publication Status
Published
Date Publish Online
2025-08-11