A focused review on recycling and hydrolysis techniques of polyethylene terephthalate

Abstract

Polyethylene terephthalate (PET) is used in textile and packaging industries. The main source of PET production is fossil fuels with limited capacity. Also, PET products are single use that transform into high volumes of wastes, causing ecosystem problems. Recycling is proposed to confront this challenge. The four major PET recycling techniques are mechanical, chemical, pyrolysis, and enzymatic. Mechanical, pyrolysis, and enzymatic techniques have constrained capabilities to manage PET waste. Chemical recycling is the potential path to expanding recycling PET waste with possibility of upcycling and addressing dirty waste streams. Several chemical methods are introduced and discussed in literature. The five major chemical recycling techniques are glycolysis, alcoholysis, aminolysis, ammonolysis, and hydrolysis. This review describes PET depolymerization via these techniques and introduces hydrolysis as the one that can depolymerize PET in an organic‐free solvent environment. Hydrolysis tolerates PET mixed wastes streams including copolymers. It helps avoid challenges attributed to using organic solvents in reaction systems. Moreover, hydrolysis produces terephthalic acid, PET monomer, which has recently gained attention as the initiative monomer for PET production. The review focuses on three forms of hydrolysis—alkaline, neutral, and acid, by presenting background studies, issued patents, and recent trends on application of hydrolysis.

Recycling and depolymerisation of poly(ethylene terephthalate): a review

“…Scheme 6 shows the reaction mechanism of PET acid hydrolysis catalysed by protonic acid. 69–71 Concentrated sulphuric acid (Scheme 7) is generally used for acid hydrolysis, and sometimes nitric acid, phosphoric acid, p -toluenesulfonic acid and ethylenediaminetetraacetic acid are also used. 27,72–74 Yoshioka believes that the hydrolysis kinetics of PET in sulphuric acid can be explained by the modified shrinking core model controlled by chemical reactions (Fig.…”

“…The mechanism of PET alkaline hydrolysis is shown in Scheme 8. 69,71,78 Usually, a solution of KOH or NaOH with a concentration of 4–20 wt% is used to treat PET waste at 200–250 °C. 12,65,79 In 1959, Pitat published a patent for the alkaline hydrolysis of PET.…”

Upcycling of Plastic Waste Using Photo-, Electro-, and Photoelectrocatalytic Approaches: A Way toward Circular Economy

“…126 Abedsoltan reported a detailed insight into hydrolysis of PET including the types and advanced treatment methodologies of the polyester plastic waste. 126 Neutral hydrolysis is used to depolymerize polyester plastic waste in excess water and high temperatures (115−420 °C) and pressures (10−420 atm), without requiring any organic solvent. 4 The kinetics and thermodynamics have been studied by Zope et al, and the frequency factor and activation energy (E a ) were found to be 2.9 × 10 8 min −1 and 9.58 kJ mol −1 , respectively, but no commercial establishment has been done due to harsh conditions and increased operational costs.…”

Acid catalyst screening for hydrolysis of post-consumer PET waste and exploration of acidolysis

“…Alkaline PET hydrolysis requires a subsequent acidification process, which is an additional step for TPA recovery not necessary for acid hydrolysis. 11 Although mineral acid catalysts have been extensively studied, their oxidative effect and tendency to cause carbonization decrease product yields. 9,[12][13][14][15] Hydrolysis can take place within 70-100 °C in the presence of highly concentrated sulfuric or nitric acids but the reaction times can extend to several days, presenting various engineering challenges.…”