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

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 (N_c,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.