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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.

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A series of aryl sulfonic acids were tested as catalysts for acid hydrolysis occurring at the surface of poly(ethylene) terephthalate (PET) particles. Specifically, p‐toluenesulfonic acid monohydrate (PTSA), 2‐naphthalenesulfonic acid (2‐NSA), and 1,5‐naphthalenedisulfonic acid tetrahydrate (1,5‐NDSA) were chosen to provide sulfonic acid active groups and varying hydrophobic functionality. The effect of catalyst concentration and reaction temperature on PET hydrolysis rate was studied. The aryl sulfonic acid catalysts exhibited much higher rates of PET hydrolysis than the mineral acid, H2SO4. At 150°C and 4 M catalyst, the time required to achieve more than 90% TPA yield was 3, 3, and 8 h, and 18 h for (PTSA), (2‐NSA), (1,5‐NDSA), and H2SO4, respectively. Ethyl acetate hydrolysis was performed as a model reaction to probe the activity of the catalysts in homogenous reactions to compare with the heterogenous hydrolysis reaction occurring at the PET surface. The higher catalytic activities for PET hydrolysis of the PTSA, 2‐NSA, and 1,5‐NDSA than H2SO4 was attributed to improved wetting by the reaction media and affinity of the aryl sulfonic acid catalysts for the PET surface.

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