H-USY and H-ZSM-5 zeolites as catalysts for HDPE conversion under a hydrogen reductive atmosphere

Abstract

The rapid increase in the consumption of plastic caused by the abrupt growth in living standards had a noticeable effect on the plastic waste generated. Consequently, a significant number of solutions have been proposed to address this issue, with catalytic cracking under H₂ atmosphere being one of the most promising ones. In this study, the catalytic conversion of HDPE under a reductive atmosphere was evaluated by thermogravimetric analysis using large and medium pore zeolites (H-USY and H-ZSM-5, respectively) with distinct Si/Al ratios as catalytic systems. The effect of adding a metallic source to zeolites was also analyzed in this work. Results show that high temperatures are required to convert HDPE (433–480 °C). However, the energy requirements can be reduced by adding a zeolite catalyst to the process. In this case, the H-USY zeolite was the most efficient catalytic system for HDPE degradation, allowing for a reduction of around 169 °C to the onset degradation temperature. The accessibility of this large pore zeolite, together with its acidic character, seems to have a determining role on the reaction. The addition of a Ni metallic source to H-USY and H-ZSM-5 led to further reduction on energy inputs. Moreover, the liquid product distribution for H-USY was shifted to lighter fractions.