Waste-to-energy : Production of fuel gases from plastic wastes

A new mechanochemical method was developed to convert polymer wastes, polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), to fuel gases (H₂, CH₄, and CO) under ball-milling with KMnO₄ at room temperature. By using various solid-state characterizations (XPS, SEM, EDS, FTIR, and NMR), and density functional theory calculations, it was found that the activation followed the hydrogen atom transfer (HAT) mechanism. Two metal oxidant molecules were found to abstract two separate hydrogen atoms from the α–CH and β–CH units of substrates, [–_βCH₂–_αCH(R)–]_n, where R = H in PE, R = _γCH₃ in PP, and R = Cl in PVC, resulting in a di-radical, [–_βCH^•–_αC^•(R)–]. Subsequently, the two unpaired electrons of the di-radical were recombined into an alkene intermediate, [–_βCH = _αC(R)–], which underwent further oxidation to produce H₂, CH₄, and CO gases.