Chemical Upcycling of Polyethylene to Value-Added α,ω-Divinyl-Functionalized Oligomers

Abstract

Today, only 9% of plastic waste is recycled worldwide, with polyethylene being one of the most frequently discarded plastics. In this work, a new route to chemically recycle polyethylene is demonstrated. Polyethylenes of two different molecular weights (M n = 1.5 kg/mol and M n = 6.6 kg/mol) were upgraded to value-added α,ω-divinyl-functionalized oligomers with shorter, tunable chain lengths via a sequence of bromination, dehydrobromination, and olefin metathesis reactions. Brominated polyethylene (BPE) was isolated in good yields (up to 86 wt %, based on PE) by direct bromination of polyethylene in air, without oxidative cleavage side-reactions. Elimination of bromide resulted in complete conversion of BPE to vinylene polyethylene (VPE) in high yields (up to 91 wt %, based on BPE). Ethenolysis of VPE afforded α,ω-divinyl-functionalized oligomers, also in high yields (up to 97 wt %, based on VPE), with carbon numbers significantly lower than those of the starting PE. Preliminary techno-economic assessments demonstrate that this three-step process could be economically viable on an industrial scale for upcycling PE into value-added chemicals that can be used in the synthesis of lubricants, as well as transformed into new commodity polymers such as polyolefins, polyethers, polyesters, and polyamides.

RETRACTED: Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts

“…Among the different strategies reported to this end, hydrogenolysis, − which utilizes H 2 to cleave the polymer into shorter alkanes, is a promising approach to deconstruct PE and PP under moderate conditions. Notably, platinum- and ruthenium-based catalysts have been shown to convert model polymers and postconsumer polyolefin plastics into liquid alkanes (C 7 –C 20+ ). − To date, these catalytic systems often require high loadings of precious metals (up to 6 wt %) and typically produce a wide array of products ranging from CH 4 and other light alkanes to liquid paraffins (C 7 –C 24 ) and solid waxes (C 25+ ), which stems from the internal C–C bond cleavage mechanism favored in these systems. − The development of catalysts that are not based on precious metals and that promote narrower product distributions would enable more efficient technologies to valorize plastic waste.…”

Chemical Upcycling of Poly(3-hydroxybutyrate) into Bicyclic Ether–Ester Monomers toward Value-Added, Degradable, and Recyclable Poly(ether ester)

“…The chemical recycling of polymers has been extensively explored, but most examples involved downcycling to produce low-molecular-weight chemicals without value-added applications. − The widely explored examples included poly­(ethylene terephthalate) (PET) (into versatile chemicals), − polylactic acid (PLA) (into lactic acid and its derivatives), , and even polyethylene (into useful liquid fuels and waxes). − In addition to the one-way chemical recycling of commodity polymers, there are numerous studies on the so-called chemically recyclable polymers with closed-loop life cycles, which can undergo a reversible polymerization/depolymerization process to realize full polymer recycling under mild conditions. − Many well-known examples of such closed-loop recycling polymers were associated with five-membered ring monomers, such as γ-butyrolactone (γBL). ,− However, the ring-opening polymerization (ROP) of five-membered ring monomers was challenging and difficult to control due to the thermodynamically stable monomer structure. Therefore, monomers with fused-ring structures were designed to modulate the ring strain energy and facilitate the reversible polymerization/depolymerization processes. ,, Moreover, the introduction of the fused ring can improve the thermal and mechanical properties of the obtained polymers for practical applications.…”

Catalytic deconstruction of waste polyethylene with ethylene to form propylene

“…Our group ( 5 ) and others ( 6 – 8 ) have been investigating catalytic chemistry that could occur with these polymers that contain only alkyl C–H and C–C bonds. Because the C–H bonds are more reactive than the C–C bonds, many efforts have focused on the introduction of functional groups onto the polymer chain to tune the properties of the plastic ( 5 , 7 , 8 ).…”

“…Because the C–H bonds are more reactive than the C–C bonds, many efforts have focused on the introduction of functional groups onto the polymer chain to tune the properties of the plastic ( 5 , 7 , 8 ). More challenging are methods for “chemical recycling” of polyolefins, which entails the cleavage of polymer chains to regenerate monomers that can be repolymerized ( 6 , 9 ). Whereas processes are well established to cleave the C–O bonds of polyesters ( 10 ), methods to cleave the alkyl C–C bonds of PE are more limited.…”