Balancing bio-oil quality and yield during rapid pyrolysis of Miscanthus using ZSM-5 and metal oxides

Abstract

Given the outstanding selective catalytic and deoxygenation abilities of ZSM-5, it has a great potential to enrich aromatics in catalytic biomass pyrolysis to oil, while metal oxides as catalysts have the ability to reduce the molecular size of compounds, which can weaken the limitation of ZSM-5 to macromolecular intermediates. In this study, metal oxides and ZSM-5 were chosen as catalysts to further extend the advantages of selective catalysis. In this paper, microscopic and bench-scale experiments for the conversion of biomass to high-yield aromatics using ZSM-5 and metal oxide catalysts were systematically investigated. In a dual catalyst pyrolysis study involving ZSM-5 and metal oxides (CaO, MgO, NiO, MoO₃), PY-GC-MS, Tube Furnace experiments were used to evaluate various catalyst layouts. The influence of catalyst dose on three-phase product yields was examined in a bench-scale fixed bed reactor employing the optimal architecture and metal oxides. The findings revealed that the dual-catalyst arrangement was critical to improving bio-oil quality. The best yield (50.02 %) of monocyclic aromatic hydrocarbons (MAHs) was produced by combining Miscanthus with the metal oxides and then separating with ZSM-5. Among the four metal oxides, CaO had the greatest synergistic effect on MAHs and selectivity. The inclusion of CaO decreased the concentration of several oxygenated compounds, particularly the suppression of furans, phenols, and acids, which was extremely advantageous for improving bio-oil quality. The highest percentage of hydrocarbon production (64.61 %) in bio-oil was produced at a Miscanthus to CaO to ZSM-5 ratio of 1:2:4, however increasing catalyst dose reduces bio-oil yield (28.92 %).