Ruthenium-catalyzed “open-loop” recycling of polyethylene via tandem isomerization-metathesis (ISOMET)†

As a model of a chemical upcycling process, we have developed a single-metal homogeneous catalytic system to break down persistent polyethylene waste into valuable chemical intermediates. This could ultimately be used to produce important chemical products, including environmentally friendly, biodegradable plastics. In the first step, a slow pyrolysis of polyolefin waste yields oils, containing long-chain olefins as the major components. Then, for the next transformation step, tailored bicyclic (alkyl)(amino)carbene (BICAAC)-Ru olefin metathesis catalysts were used in combination with an alkene isomerization catalyst (RuHCl(CO)(PPh₃)₃) for the transformation of the pyrolysis oil to propylene via isomerization-metathesis (ISOMET) reaction in ethylene atmosphere. Eventually, translation of the highly efficient single-metal catalyst system enabled ISOMET reaction to a 900 mL reactor setup and repetitive batch experiments could prove the long-term stability of the catalyst system and the highest total turnover number (tTON = 2788 mol propylene per mol olefin metathesis catalyst) reported so far using post-consumer polyethylene waste feedstock.