Chemical Recycling of Polystyrene to Valuable Chemicals via Selective Acid-Catalyzed Aerobic Oxidation under Visible Light

• Zhiliang Huang^a
• Muralidharan Shanmugam^b
• Zhao Liu^c
• Adam Brookfield^b
• Elliot L. Bennett^a
• Renpeng Guan^a
• David E. Vega Herrera^a
• Jose A. Lopez-Sanchez^a
• Anna G. Slater^a
• Eric J. L. McInnes^b
• Xiaotian Qi*^c
• Jianliang Xiao^a

• ^aDepartment of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
• ^bDepartment of Chemistry and Photon Science Institute, The University of Manchester, Manchester M13 9PL, U.K.
• ^cEngineering Research Center of Organosilicon Compounds & Materials, Ministry of Education, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, P. R. China

Chemical recycling is one of the most promising technologies that could contribute to circular economy targets by providing solutions to plastic waste; however, it is still at an early stage of development. In this work, we describe the first light-driven, acid-catalyzed protocol for chemical recycling of polystyrene waste to valuable chemicals under 1 bar of O2. Requiring no photosensitizers and only mild reaction conditions, the protocol is operationally simple and has also been demonstrated in a flow system. Electron paramagnetic resonance (EPR) investigations and density functional theory (DFT) calculations indicate that singlet oxygen is involved as the reactive oxygen species in this degradation process, which abstracts a hydrogen atom from a tertiary C–H bond, leading to hydroperoxidation and subsequent C–C bond cracking events via a radical process. Notably, our study indicates that an adduct of polystyrene and an acid catalyst might be formed in situ, which could act as a photosensitizer to initiate the formation of singlet oxygen. In addition, the oxidized polystyrene polymer may play a role in the production of singlet oxygen under light.

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