Catalytic deconstruction of waste polyethylene with ethylene to form propylene

Abstract

The conversion of polyolefins to monomers would create a valuable carbon feedstock from the largest fraction of waste plastic. However, breakdown of the main chains in these polymers requires the cleavage of carbon–carbon bonds that tend to resist selective chemical transformations. Here, we report the production of propylene by partial dehydrogenation of polyethylene and tandem isomerizing ethenolysis of the desaturated chain. Dehydrogenation of high-density polyethylene with either an iridium-pincer complex or platinum/zinc supported on silica as catalysts yielded dehydrogenated material containing up to 3.2% internal olefins; the combination of a second-generation Hoveyda-Grubbs metathesis catalyst and [PdP( t Bu) 3 (μ-Br)] 2 as an isomerization catalyst selectively degraded this unsaturated polymer to propylene in yields exceeding 80%. These results show promise for the application of mild catalysis to deconstruct otherwise stable polyolefins.

Catalytic Chemical Recycling of Post-Consumer Polyethylene

“…Abu-Omar and co-workers incorporated unsaturation into commercial polyethylene via stoichiometric bromination and dehydrobromination, followed by ethenolysis to form low-molecular-weight divinyl-terminated polyethylene as value-added products (Figure c) . Recently, Hartwig and co-workers, and Guironnet, Scott and co-workers catalytically deconstructed polyethylene through transfer dehydrogenation, isomerization, and metathesis into propylene (Figure d). , In this work, dehydrogenated HDPE was used to develop recyclable-by-design polyethylene-like materials from hard-to-recycle waste HDPE (Figure ).…”

“…48 Recently, Hartwig and co-workers, and Guironnet, Scott and co-workers catalytically deconstructed polyethylene through transfer dehydrogenation, isomerization, and metathesis into propylene (Figure 2d). 49,50 In this work, dehydrogenated HDPE was used to develop recyclable-bydesign polyethylene-like materials from hard-to-recycle waste HDPE (Figure 1).…”

Understanding the Structure–Activity Relationships in Catalytic Conversion of Polyolefin Plastics by Zeolite-Based Catalysts: A Critical Review

“…For example, Guironnet and Peters proposed a kinetic model of a new polyethylene conversion approach which consists of tandem olefin metathesis and double-bond isomerization for selective depolymerization to propylene . Excitingly, this simulated path was recently successfully verified by Conk et al using well-designed homogeneous catalytic systems or by Wang et al using a multifunctional heterogeneous catalyst, respectively . In Wang’s work, they use Pt/Al 2 O 3 as a dehydrogenation catalyst and commercial MTO catalyst as an olefin metathesis catalyst.…”

Towards a Cradle‐to‐Cradle Polyolefin Lifecycle

“…The recent publication by Conk et al [7] . brings us a step closer to the goal of selective depolymerization.…”

“…% for ethylene from a low linear density polyethylene (PE) feed, achieved via a high temperature two-step pyrolysis/catalytic cracking process. [6] The recent publication by Conk et al [7] brings us a step closer to the goal of selective depolymerization. By using a tandem reaction strategy, the study demonstrates that PE can be depolymerized to propylene with yields as high as 87 % (Figure 1A).…”