Aromatic production from high-density polyethylene over zinc promoted HZSM-5.

The nature of Zn species and their roles in catalytic cracking of high-density polyethylene (HDPE) thermal decomposing vapor over Zn-promoted HZSM-5 (Zn/Z5) for aromatics were investigated. The Zn/Z5 zeolites were prepared using ion exchange and impregnation methods followed by H 2 reduction. Results indicated that hydrogen reduction of the Zn/Z5 significantly improved the aromatic yield. [ZnOH]+ and bridged Zn2+ species were critical species promoting BTX formation, with the former demonstrating higher activity. Besides, the synergistic effect between the Zn species and Brønsted acid sites on HZSM-5 boosts the aromatic yield. Incorporation of Zn was also found to promote long-chain scission. Among all the Zn/Z5, hydrogen reduced 2 wt% Zn/Z5 (SAR=25) is most effective in producing BTX, with a maximum yield of BTX (48%) and BTX selectivity (93%); hydrogen reduced 2 wt% Zn/Z5 (SAR=50) produced the highest yield of total aromatics (53%). [Display omitted] • First investigation on nature and roles of Zn species on HDPE aromatization. • [ZnOH]+ was found to have the greatest contribution in promoting aromatization. • Incoporation of Zn also promoted the cracking of long-chain intermediate. • H 2 treatment is vital to improving BTX yield by optimizing Zn species distribution. • A maximum of 53% aromatic yield and a 93% BTX selectivity were obtained. [ABSTRACT FROM AUTHOR]