Depolymerization of waste polyethylene to linear alkenes via sequential dehydrogenation and metathesis

Polyethylene (PE) is the most abundantly sourced plastic and significant efforts are needed for its end-of-life management. The deconstruction of PE is an uphill task and requires the breaking of highly stable C–C bonds. Here we demonstrate that PE can be deconstructed to value-added dodecene, along...

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Published inGreen chemistry : an international journal and green chemistry resource : GC Vol. 26; no. 20; pp. 10558 - 10566
Main Authors Khopade, Kishor V., Rajput, Nikhita S., Rangappa, Raghavendrakumar, Barsu, Nagaraju, Chikkali, Samir H.
Format Journal Article
LanguageEnglish
Published Cambridge Royal Society of Chemistry 14.10.2024
Subjects
Alkenes
Covalent bonds
Decomposition reactions
Dehydrogenation
Depolymerization
End of life
Gel chromatography
High temperature
Infrared spectroscopy
Iridium
Iridium compounds
Metathesis
NMR
Nuclear magnetic resonance
Plastic debris
Polyethylene
Polyethylenes
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Summary:Polyethylene (PE) is the most abundantly sourced plastic and significant efforts are needed for its end-of-life management. The deconstruction of PE is an uphill task and requires the breaking of highly stable C–C bonds. Here we demonstrate that PE can be deconstructed to value-added dodecene, along with other long-chain alkenes. The PCP–iridium complex catalyzes the dehydrogenation of commercial and post-consumer polyethylene waste to produce dehydrogenated polyethylene (DHP) with 0.5–1.0% unsaturation. The DHP was subjected to an ethylene cross-metathesis reaction in the presence of suitable catalysts. Through meticulous optimization of reaction parameters, 63% selectivity toward dodecene, with 26% overall yield, was achieved. The practical significance of our method has been demonstrated by subjecting post-consumer plastic waste to dehydrogenation followed by ethylene metathesis to produce dodecene as a major product, together with long-chain alkenes. The PE deconstruction has been confirmed by recording molar mass before and after depolymerization using high-temperature gel permeation chromatography. The existence of dodecene has been unambiguously ascertained using GC, GC-MS, NMR, and IR spectroscopy. Thus, these results demonstrate the conversion of waste PE to value-added dodecene and long-chain alkenes under mild reaction conditions.
ISSN:1463-9262
1463-9270
DOI:10.1039/D4GC03646H