Catalytic cracking of LDPE over nanocrystalline HZSM-5 zeolite prepared by seed-assisted synthesis from an organic-template-free system

Abstract

The catalytic cracking of low density polyethylene (LDPE) was accomplished using nanocrystalline HZSM-5 zeolites. Nanocrystalline ZSM-5 zeolites were synthesized by a seed-assisted method from an organic-template-free system employing three different seeding strategies: two of these strategies based on aqueous clear solutions containing the ZSM-5 precursors (silanized and non-silanized) and the third strategy based on a commercial ZSM-5 zeolite in powder form. The plastic cracking reactions were carried out at 380–420°C, employing really mild conditions (plastic to catalyst mass ratio of 100). Nanocrystalline HZSM-5 zeolites prepared by seed-induced synthesis based on liquid solutions exhibit a superior catalytic activity than the reference microcrystalline zeolite. Conversion values very close to 100% are achieved at 420°C, by using these catalysts, while significant conversion values (>50%) are still attained at 380°C. Moreover, these nanocrystalline HZSM-5 zeolites promote the production of a high proportion of light olefins (>60% at 380°C), propylene, 1-butene, isobutene, being the main products (∼50%). Nanocrystalline HZSM-5 synthesized from a clear solution containing an organic structure-directing agent (TPA+) exhibits a 100% conversion value at 380°C. However, the economic and environmental advantages of the seed-assisted synthesis from a TPA+ free system and the remarkable activity showed by the nanocrystalline zeolites obtained, makes of these materials interesting catalysts in the LDPE catalytic cracking.