Catalytic pyrolysis of biomass to produce aromatic hydrocarbons in a cascade dual-catalyst system: Design of red mud based catalyst assisted by the analysis of variance

Abstract

Theoretical and experimental study on the catalytic pyrolysis of rape straw was carried out for the production of aromatic hydrocarbons using the composite red mud (RM) and zeolite HZSM-5 catalyst as the combined catalysts. In the orthogonal tests and analysis of variance (ANOVA), it was originally established that Fe2O3 and CaO acted as the active metal oxides in the red mud, which played the notable role in the production of benzene, toluene and xylene (BTX) as hydrocarbon fuels. Subsequently, the physicochemical property of the Fe2O3 and CaO loaded red mud (Fe2O3-RM and CaO-RM) was investigated and their performance in the catalytic pyrolysis of rape straw combined with HZSM-5 were investigated. It was revealed that the further cracking of the primary pyrolysis gas was promoted with more active Fe2O3 involved, and the heavy component was converted into the light fraction entering HZSM-5 for deoxygenation and aromatization to produce aromatic hydrocarbons. The yield of BTX over Fe2O3-RM was boosted by 10.15 wt% compared with the original red mud catalyst, while that of BTX was further promoted to 11.37 wt% over the composite red mud catalyst with 6% CaO loading. In addition to the strong bond-breaking performance of CaO, calcium carboxylate was easily generated and then decomposed to form CaCO3 and ketones, and then BTX were produced from ketones over HZSM-5 by deoxygenation and aromatization. In this study, the high-performance red mud-based catalysts was designed and utilized in the thermochemical conversion of biomass, providing a potential way for the utilization of two solid wastes, rape straw and red mud to produce hydrocarbon fuels in a high-valued way.