Aromatics production with metal oxides and ZSM-5 as catalysts in catalytic pyrolysis of wood sawdust

Abstract

Dual catalysts are proposed in this study to convert biomass pyrolysis vapors into aromatics. Metal oxides (CaO, Al2O3, and ZnO) and ZSM-5 were introduced into the catalytic upgrading process. In the pyrolysis process without ZSM-5, the addition of CaO effectively removed carboxylic organics and methoxyphenols, reducing the product yield with a hydrogen to carbon ratio of 0, and the size of phenol compounds. The addition of Al2O3 greatly promoted the cracking of oxygenates with molecular weight above 109 g mol−1, such as large-size methoxyphenols and sugars. It is found that the upgraded pyrolysis volatiles are more conducive to conversion for aromatics with a ZSM-5 catalyst. The addition of CaO increased the selectivity of xylene (15.9%), while Al2O3 promoted the selectivity of toluene (18.3%). The highest yield of aromatics was obtained with CaO-ZSM-5 dual catalyst system, which was boosted by 6.14% compared to that of pure ZSM-5. To explore more effective methods for aromatics production, the arrangement of catalysts and temperature condition were investigated. Mixing CaO with biomass produced more aromatics than other methods, and the most suitable temperature for the formation of aromatic hydrocarbons was 600 °C.