Highly selective production of aromatics via co-pyrolysis of pine sawdust and polypropylene in binary molten chlorides combined with commercial HZSM-5 catalysts

Biomass catalytic pyrolysis for the production of aromatics as an alternative to petrochemical resources is a promising technology in the context of carbon neutrality. The aromatization of furans presents a novel pathway for converting biomass into aromatics. In this study, four binary molten chlorides (NaCl-FeCl2, NaCl-MnCl2, NaCl-ZnCl2, and NaCl-MgCl2) were selected for the pyrolysis of pine sawdust. The thermal stability and eutectic points of the binary molten chlorides were tested by TG-DSC. The introduction of binary molten chlorides significantly increased the selectivity for furans in bio-oil, reaching 72.2-91.8 area% for NaCl-ZnCl2 and 42.8-71.2 area% for NaCl-FeCl2. Commercial HZSM-5 was characterized by SEM, XRD, BET, NH3-TPD, and PyIR, and HZSM-5/cordierite monolithic catalysts were prepared. Co-pyrolysis of pine sawdust and polypropylene in binary molten chlorides were conducted, combined with in-situ or ex-situ catalytic processes. Furans generated from the pyrolysis of pine sawdust in binary molten chlorides served as key intermediates for the production of aromatics with high selectivity in a single step. In ex-situ catalytic pyrolysis, the highest selectivity for aromatics reached 91.2 area%. The van Krevelen diagram indicated that the aromatics from bio-oil had the potential to substitute ethylene tar in carbon black production. Diels-Alder reactions were discussed in the proposed reaction pathways for catalytic co-pyrolysis.