(538q) The Olefin-Intermediate Process (OIP): A Means to Depolymerize & Upcycle Waste Plastics

Over eight billion metric tons of plastic was created between 1950 and 2015, and this figure is expected to double in the next three decades¹. Accumulation of plastic in our landfills, waterways and oceans, whether in the form of plastic bags, micro-plastics, or other waste, is becoming a critical issue^1,2. The current status of our recycling technology is not capable of solving this problem. New technologies, developed through fundamental research, are thus required to develop robust and cost-effective recycling strategies. We recently proposed a new approach in the depolymerization of waste plastics, which we called, the Olefin-Intermediate Process (OIP)^3,4. The OIP is a platform concept where feedstocks like polyolefin plastics are ‘activated,’ producing an olefin intermediate. This olefin can then be reacted with an orthogonal chemistry, often described as a tandem chemistry, that results in new reaction pathways to products⁵. Though the phraseology of this concept has yet to gain wide adoption, the prevalence of this reaction concept is becoming increasingly common in the plastics catalysis community. For example, the Marks Group recently demonstrated an OIP that utilized a metal triflate and supported palladium catalyst system, which was capable of depolymerizing condensation polymers like polyethylene terephthalate⁶. Similarly, the Scott Group recently proposed a tandem system where aromatization and hydrogenolysis were coupled to produce branched aromatics from polyethylene at relatively mild process conditions (a process that closely resembles an OIP)⁷. In this presentation, I will outline the concept of the OIP, discussing the definition and presenting several examples in the literature. Subsequently, I will present an update on our research efforts in the use of an OIP that leverages a fully heterogeneous, tandem, catalyst system that couples dehydrogenation and olefin metathesis to depolymerize polyethylene feedstocks at temperatures < 200°C. For example, at 200°C, with excess n-pentane solvent, we achieved 42% conversion of a 5 wt.% (^g/_g) n-eicosane (a model compound for polyethylene) in 15 hr. The products from this reaction are a distribution of low molecular weight liquid alkanes. Applications to polyethylene (M_w = 54 ± 2 kDa) have demonstrated significant accumulation of liquid alkane products with a demonstrated 73% reduction in molecular weight. I will also discuss the role of pretreatment process and certain promoters that can significantly enhance catalytic activity.

References

1. Geyer, R., Jambeck, J. R. & Law, K. L. Production, use, and fate of all plastics ever made. Sci Adv 3, 1–5 (2017).
2. Jambeck, J. R. et al. Plastic waste inputs from land into the ocean. Science 347, 768–771 (2015).
3. Ellis, L. D. et al. Tandem heterogeneous catalysis for polyethylene depolymerization via an olefin-intermediate process. ACS Sustain. Chem. Eng. 9, 623–628 (2021).
4. Ellis, L. D. et al. Chemical and biological catalysis for plastics recycling and upcycling. Nat. Catal. 4, 539–556 (2021).
5. Lohr, T. L. & Marks, T. J. Orthogonal tandem catalysis. Nat. Chem. 7, 477–482 (2015).
6. Kratish, Y. & Marks, T. J. Efficient Polyester Hydrogenolytic Deconstruction via Tandem Catalysis. Angew. Chem. Int. Ed. 61, (2022).
7. Zhang, F. et al. Polyethylene upcycling to long-chain alkylaromatics by tandem hydrogenolysis/aromatization. Science 370, 437–441 (2020).