Opening up ZSM-5 Hierarchical Zeolite’s Porosity through Sequential Treatments for Improved Low-Density Polyethylene Cracking †

Abstract

An adequately tuned acid wash of hierarchical ZSM-5 zeolites offers a levelling up in the catalytic cracking of low-density polyethylene. Identification of crucial and limiting factors governing the activity of the zeolite was extended with studies about the accessibility of acid sites, nature of the realuminated layer and role of Lewis acid sites. The sequential treatment of a ZSM-5 zeolite offered enhanced activity in low-density polyethylene (LDPE) cracking at low and high conversions, as confirmed by a decrease in the temperatures needed to reach 20% and 80% conversion (T ₂₀ and T ₈₀, respectively). A linear dependence of the T ₈₀ on the coupled IHF (indexed hierarchy factor) and AF _B (accessibility factor) highlighted the importance of the textural and acidic parameters in the catalytic cracking of LDPE. Operando FT-IR-GC studies confirmed a higher fraction of short-chain hydrocarbons (C ₃–C ₅) in the product distribution of hierarchical catalysts resulting from the effective polymer cracking in easily accessible pores.