Co-hydropyrolysis of pine and HDPE over bimetallic catalysts: Efficient BTEX production and process mechanism analysis

Abstract

Co-pyrolysis of plastics and biomass is expected to replace traditional petroleum processing to produce BTEX (benzene, toluene, ethylbenzene, and xylenes) on a large scale, which are important chemical raw materials. The introduction of bimetallic catalysts and hydrogen in co-pyrolysis systems is an effective strategy to increase the content of aromatic hydrocarbons in pyrolysis oils, which has not been studied so far. The present study investigated the efficacy of bimetallic catalysts in enhancing aromatization and Diels-Alder reactions in comparison to Mo/ZSM-5. The synergistic interaction between bimetals contributed to the improved selectivity of aromatic hydrocarbons, particularly BTEX. Results revealed that NiMo/ZSM-5 catalysts led to higher aromatics selectivity in liquid oil, whereas FeMo/ZSM-5 resulted in higher BTEX selectivity in aromatic hydrocarbons. Moreover, metal oxide-supported bimetallic catalysts exhibited lower selectivity for aromatic hydrocarbons in liquid oil, despite facilitating higher liquid-oil yield. Among the metal oxide-supported bimetallic catalysts, FeMo/TiO2 demonstrated the highest selectivity (56%) for aromatic hydrocarbons in liquid oils. The introduction of hydrogen resulted in 100% selectivity of BTEX in aromatic hydrocarbons, thus highlighting the significance of hydrogenation in enhancing the selectivity of BTEX. Combined with the experimental results and literature, a possible reaction mechanism was also proposed.