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 (T20 and T80, respectively). A linear dependence of the T80 on the coupled IHF (indexed hierarchy factor) and AFB (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 (C3–C5) in the product distribution of hierarchical catalysts resulting from the effective polymer cracking in easily accessible pores.
Highlights
Hierarchical zeolites are known to efficiently crack polymers or vacuum gas oil, giving high selectivity to most desirable products [1,2,3,4,5]. The benefits to these cracking reactions are the combination of a secondary mesopore system coupled with the intrinsic acidity of microporous zeolites [6,7]
Demetallation processes, i.e., desilication and dealumination, are highly versatile methods of hierarchical zeolite preparation; appropriately defined modification conditions ensure that hierarchical porosity can be obtained independently of Si/Al ratio, structure type or grains size [10,11]
The catalytic low-density polyethylene (LDPE) cracking results showed that the zeolites modified in a sequential manner (deSi-ZSM-5&Ac(*)) were significantly more active in comparison to the desilicated cases
Summary
Hierarchical zeolites are known to efficiently crack polymers or vacuum gas oil, giving high selectivity to most desirable products [1,2,3,4,5]. The benefits to these cracking reactions are the combination of a secondary mesopore system coupled with the intrinsic acidity of microporous zeolites [6,7]. Demetallation processes, i.e., desilication and dealumination, are highly versatile methods of hierarchical zeolite preparation; appropriately defined modification conditions ensure that hierarchical porosity can be obtained independently of Si/Al ratio, structure type or grains size [10,11].
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