Cost-effective synthesis of hierarchical HZSM-5 with a high Si/TPA+ ratio for enhanced catalytic cracking of polyethylene

Abstract In this work, hierarchical HZSM-5 zeolites, with the high Si/TPA+ ratio of 34 and Si/Al ratios of 100 and 30, have been synthesized by the mesoporogen-free, Na+-free, and steam-assisted crystallization route using industrial silica sol as the silicon source. Highly crystalline HZSM-5 (30)-34 sample inherited the strong acidity of conventional HZSM-5 and exhibited the relatively large mesopore volume (0.08 ​cm3 ​g−1). With this structure, the accessibility of Bronsted acidity sites is increased from 6.25% of conventional HZSM-5 to 64.3% of HZSM-5 (30)-34, which enhanced the catalytic cracking performance of low-density polyethylene (LDPE). As a result, the decomposition temperature of LDPE was reduced to 420 ​°C, which is apparently lower than 482 ​°C when no catalyst was adopted. Moreover, the HZSM-5 (30)-34 sample showed good reusability and catalytic stability in the regeneration-recycle experiments.