Catalytic fast pyrolysis of bamboo sawdust via a two-step bench scale bubbling fluidized bed/fixed bed reactor: Study on synergistic effect of alkali metal oxides and HZSM-5

Abstract

Catalytic fast pyrolysis of bamboo sawdust was conducted by a tandem bubbling fluidized bed/fixed bed reactor. Effect of pyrolysis and catalyst temperatures on product yield was studied. In addition, synergistic effect of HZSM-5 and base catalysts (including CaO, MgO, and SrO) for the promotion of aromatic hydrocarbons was revealed. Experimental results illustrated that both pyrolytic and catalytic reactor temperatures played pivotal roles in the yield of bio-oil, and the optimal pyrolysis and catalytic reactor temperatures were 550 °C and 500 °C, respectively. Ex-situ catalytic trial decreased the yield of bio-oil compared to in-situ run, while it facilitated the formation of phenol and alkylphenols. Mixed catalytic upgrading modes exhibited more significant aromatization and deoxygenation activities than sequential ones. In particular, ex-situ run using CaO mixed with HZSM-5 increased the concentration of aromatic hydrocarbons to 31.34%, which was ∼11.48% higher than that derived from CaO and HZSM-5 sequentially processed mode. The dominated products in alkylphenols were cresol isomers and ethylphenols, and compared to sequential cases, mixed catalytic upgrading trials promoted the relative selectivity of phenol. Synergistic effect of base catalysts and HZSM-5 contributed to the production of monocyclic aromatic hydrocarbons, and CaO mixed with HZSM-5 mode showed the most prominent synergistic effect for the enhanced relative selectivity to xylenes and toluene.