Selective Upcycling of Waste Polyethylene into Propane Facilitated by the Undulation Confinement Effect in Zeolite Channels.

Selective conversion of polyethylene (PE) into high-value bulk chemicals holds significant industrial application value. However, the uniform C-C bonds in the PE main chain render directed cleavage a formidable challenge. Here we developed a channel undulation-confinement hydrocracking (CUCH) strategy, achieving selectivity of propane up to 70.2% from PE conversion using a ZSM-5 zeolite catalyst. This selective conversion process originates from the deep β-scission of C-C bonds and the match of propane molecular size with the channel undulation factor (Ω = 0.71) of ZSM-5. Reaction kinetics analysis, thermodynamics and theoretical calculation reveal that Brønsted acid sites donate protons to activate PE, initiating C-C bonds cleavage to form alkanes and tricoordinated carbenium ions. Concurrently, the cracking degree of these carbenium ions is modulated by undulation factor (Ω) and the number of intracrystalline cages (Nc,s) in zeolite. This double confinement prolongs the residence time of C4+ intermediates, maximizing their cracking and enhancing the ultimate yield of propane. These findings provide a feasible strategy for the selective upcycling of waste PE.