Recycling of polystyrene waste to mono-aromatic hydrocarbons via intermittent thermal scission

Abstract

Polystyrene (PS) is a widely used plastic that contributes significantly to plastic waste. Chemical recycling of PS into valuable industrial mono-aromatic hydrocarbons (MAHs) offers a promising approach for mitigating the environmental impact of PS waste while simultaneously valorizing it. However, current methods typically achieve MAH yields of less than 75%, with limited potential for significant improvement. Here, we propose a novel cyclic depolymerization and repolymerization strategy to precisely control PS pyrolysis without catalysts. This method alternates depolymerization at around 400 °C with repolymerization at around 300 °C in a semi-batch system, achieving an unprecedented MAH yield (MAH selectivity up to 95% with liquid yields exceeding 90 wt%). Repolymerization forms cross-linked structures, effectively suppressing oligomer formation and converting low-reactivity oligomers into more reactive polymer segments, which is crucial for achieving extraordinarily high MAH yields. This “intermittent” scission strategy is broadly applicable to diverse PS waste streams, highlighting its potential for sustainable waste management.