Enhanced production of monocyclic aromatic hydrocarbons by catalytic pyrolysis of rape straw in a cascade dual-catalyst system of modified red mud and HZSM-5

Catalytic pyrolysis of rape straw was carried out on a dual-catalyst system to produce benzene, toluene, xylene (BTX), realized by promoted cracking of large-molecule pyrolysis vapor over red mud (RM) and followed by selectively catalytic conversion over HZSM-5. With the pyrolysis temperature of 550 °C and the catalyst/biomass mass ratio of 2:1, the yield of BTX in bio-oil reached the maximum of 10.27 wt%. The coking resistance of HZSM-5 in the cascade catalytic system was obviously better than pure HZSM-5. The pretreatment of RM by calcination and acid washing was also performed. The unstable components of RM like cancrinite were decomposed during the calcination. Besides, the content of active metal oxides in RM after acid washing increased by removing Na2O and CaO. Its specific surface area was promoted, due to the new micropores caused by the dispersion of dissolved metal oxides. RM treated with 3 mol/L hydrochloric acid presented the highest specific surface area of 55.24 m2/g while the maximized yield of BTX of 12.91 wt%. Therefore, the dual-catalyst system might be an effective method to dispose and high valued use of rape straw and RM as solid wastes with significant environmental impact to promote carbon neutrality.